3 Reasons Why You Can't Act Your Age Around Your Siblings

Do you find yourself 'regressing' in the presence of your siblings? Here's the science behind it.

By Mark Travers, Ph.D. | February 05, 2025

Do you ever notice that no matter how much you feel like a "real adult," you can never seem to get it right when it comes to your siblings? Even on days when you come to family gatherings with the very best intentions, your siblings seem to have an almost magical ability to turn you into a younger version of yourself that could be people-pleasing, emotionally immature or even petty—almost like you're ten years old all over again.

If so, you're not alone. Many people feel like their family knows just the right buttons to push to elicit tantrums and screaming matches reminiscent of their childhood that feel far-removed from the person they've grown to be. Resentment toward siblings often stems from years of unresolved trauma, making these issues some of the hardest to overcome and leave behind.

Our siblings are often the people who have known us the longest, and if rebuilding a civil relationship with them does not put you at risk, it could significantly improve your quality of life. That's why it's worth exploring the underlying animosity between you, to uncover why letting go and moving forward might feel so difficult, and to feel realigned with your true self.

Here are three reasons why you may struggle to act like an adult in sibling relationships, and how to move past it.

1. Your Parents Could Be Adding To The Tension

Parents often create personal narratives for their children. This is not always intentional, but is undoubtedly recognized by the children in the house. Perhaps a parent always comments on how bright or beautiful one child is, but does not pay the other child in the house the same compliment. This comparison could affect the second child's perception of themselves.

Parents who view one child in a more favorable light are also more likely to treat that child differently without even realizing it. Research published in the Journal of Youth and Adolescence in 2018 suggests that when it comes to discipline and parent-child conflict, a child who is viewed more positively is likely to be given the "benefit of the doubt," whereas the "naughty child" receives stricter punishment.

Over time, children can internalize this differential treatment, driving a deep wedge between them. The favored child may also align with the parents, viewing their brother or sister as the problem, while the less favored child may develop a "me vs. them" mindset. The resulting resentments can linger well into adulthood.

2. You Still View Yourself From The Perspective Of Your Birth Order

Do you ever look at your little brother or sister and still see the baby your mom brought home from the hospital—even if they are now a grown man or woman? While endearing in it's own way, it could be part of the problem you're having in your sibling relationships.

A 2023 study highlights that older siblings are less likely to feel inferior to their younger siblings, sometimes even stepping into a more parental role with them. However, while many older siblings hold strong opinions about how their younger counterparts should behave, younger siblings begin looking to the world around them to form their own beliefs and opinions as they grow older. If these views clash, it can lead to long-term friction in the relationship.

While you may view yourself in many ways as responsible for the "baby" of the house, the truth is that they are now a grown adult who would prefer that you do not dictate their lives—even if you believe you know better.

In contrast, as a younger sibling or middle child, you may find yourself automatically falling into the role you played as a child—whether that was the "baby" who needed protection, the "troublemaker" who always stirred the pot or the "peacemaker" who tried to smooth things over. These ingrained roles can be difficult to shake, even when you've long outgrown them in other areas of your life.

3. You're Playing Your Childhood 'Role'

The black sheep, the golden child, the invisible one—these are just a few of the roles that adults, whether knowingly or unknowingly, assign to children. The problem with these labels is that they can be hard to escape and have long-standing effects.

For instance, a 2020 paper published in The Family Journal highlights that individuals who take on the role of the rebellious "scapegoat" and the overlooked "lost child" due to familial dysfunction often struggle with depressive symptoms later in life.

When siblings continue to define themselves—and each other—by these roles and labels, they naturally regress into the version of themselves they were assigned to. Continuing to play the role also keeps the dysfunctional family system consistent, if not conflict-free. Embracing change, no matter how positive, can shake up family dynamics for good, which can be an intimidating adjustment to make.

One of the most overlooked reasons why sibling dynamics remain tense is that they often serve as a mirror for unresolved emotional wounds from childhood. If you felt unheard, overshadowed or undervalued growing up, you may still carry those emotions into your interactions with your siblings—whether or not they are still relevant today.

Healing these wounds requires recognizing the patterns at play and working to separate past hurts from present realities. By addressing the emotions beneath the surface, you can begin to interact with your siblings as they are now, rather than through the lens of childhood grievances.

How To Resolve Adult Sibling Rivalry

If you notice these patterns in your sibling relationship, it's important to remember that you can break them and rewrite the narrative of your bond. Research from the University of Illinois highlights the numerous benefits of maintaining a close relationship with siblings in adulthood. One key advantage is the psychological and practical support they can offer in your daily life.

Here are a few ways to improve your relationship with your sibling:

• Let go of the comparison. Siblings can experience the same parents in vastly different ways due to factors like birth order, personality differences or shifting family circumstances. For instance, if a parent faced financial hardship, personal struggles or emotional growth over the years, they may have treated each child differently without intending to. Rather than letting parental dynamics create distance, focus on how you and your sibling relate to each other as individuals now.
• Set clear boundaries. Have a conversation with your sibling in which you each acknowledge the past and create boundaries that help you break free of the roles and responsibilities allocated to you in childhood. It's alright if this process takes time.
• Let go of the competition. You and your sibling live independent lives, so competing for attention, approval or success is unnecessary. Shift your focus from comparison to collaboration, and celebrate each other's achievements without giving in to resentment. Remember, you are not your younger selves, and things can look different now.

Your sibling is usually your first friend and can be a lifelong companion if you treat each other right. While these relationships can be challenging, they also have the potential to be incredibly rewarding.

Understanding the deeper reasons behind your conflicts can help you break free from old patterns and rebuild your connection on a healthier, more mature foundation. After all, your sibling may be one of the few people who truly understands your history—so if reconciliation is possible, it may be well worth the effort.

Do you have a difficult relationship with your sibling because you felt responsible for them? Take this science-backed test to find out: Parentification Scale

A similar version of this article can also be found on Forbes.com, here.