Tbh, having been there, from age 17-21 you're more or less the same as each other. You'll still fall in with the students fresh out from school once you start, whereas the "true" mature students (i.e. those that are usually 30+ years, or in their mid-late 20s with family commitments etc) tend to decide for themselves how much they want to integrate into the social life.
Basically, don't worry about it. Even if you were in you were in the much older age groups you could well integrate into student life if you so chose. The mature students who don't, more than anything are doing so out of choice as they have their own social groups outside of the university.