Learn English – Can we grow a habit

This works just fine:

I think you've become too dependent on your parents, and you don't want to move on.

There are plenty of other ways you can say this, of course. You might be interested in this more idiomatic way:

Dude, you are 24 and still live with your parents. It's time to get loose from those apron strings.

The expression tied to your mother's apron strings means that you are too dependent on your mother, especially when it would be more appropriate to start gaining more independence in your life.

UE says:

A man who is tied to a woman's apron strings is excessively dependent on her, especially when it is his mother's apron strings.

A page at encyclopedia.com reveals:

apron strings, tied to one's mother's traditional phrase, meaning that a person who should be grown up is still subject to their mother's dominance;
_{from the mid 16th century, an apron string as the fastening of an apron has been used to symbolize the role of the mistress of a household}

Another common English idiom comes straight from avian science:

You're still 24 and you live with your parents. I think it's time they kick you out of the nest.

The nest is a common metaphor to use for the home, particularly when discussing the topic of grown children leaving. For example, one Investopedia headline reads: Why Some Kids Never Leave The Nest, while The CSM asks: Adult kids at home: Time to kick the birds out of the nest?

Generally speaking, the kicking-out-of-the-nest expression addresses the issue more from the perspective of the parents.

You are correct in your observation that the definition of "pastime" already includes the definition of "activity", hence using "pastime activity" is redundant. This type of phrase is called a pleonasm and is common when speakers aren't aware of the correct meaning of the word, or simply by mistake. More common pleonasms include "CD disc" or "LED diode" (caused by unawareness of the abbreviation).

If used as a mistake (like in this case), pleonasm is a stylistic error. If you want to use it as a literary tool (to express natural speech for example), it is fine, but otherwise using simply "pastime" is more correct.