Here are some pitfalls that might occur if there is too much of a maturity gap in your relationship:

You might feel frustrated, like the relationship isn’t going anywhere
You might feel like you are always making the decisions
You could feel like an emotional garbage disposal – your partner looks to you to solve all of his/her problems
You might feel like your partner never takes things (including you and the relationship) seriously
You might feel like you don’t have much in common with your partner’s friends and maybe even that they are a bad influence
You might feel like you will never get the type of commitment from your partner that you want
You might feel like you take on the bulk of the responsibility and planning for your lives
You might feel like it’s impossible to have a productive argument with your partner
You might feel like you are always taking care of him/her financially
You might feel like you are watching a train wreck, as your partner makes the same mistakes over and over again
On the same token, if you are the less mature member in the relationship, things might be tough for you too. For example, you might:

Feel like your partner is always telling you what to do
Feel like your partner talks down to you
Feel like you are being pushed into a serious commitment before you are ready
Feel like your partner never wants to just relax and have fun
Feel like your partner sees you as a child instead of as a companion
Feel like your partner doesn’t trust you to complete tasks but then resents you for not contributing
Feel like you and your partner are in different life stages and want different things
Feel like you have to rush your timeline for things like marriage and kids to accommodate your partner’s timeline
Feel like you are missing out on crucial years of fun and freedom
So, you see, problems can arise from both sides of the fence. Still, I’m not saying that age gap relationships can’t work.

What is too much of an age gap for one relationship may not be just right for another. And large age gaps in relationships can be successful, as long as both partners are willing to put in the work.