Hi, as a mature student looking to go to university. One advice i can give you is always look ahead and not backwards. You cannot change the past so live life how you want to in the present. Go join clubs, societies, sports etc. and meet like minded people. Or, if you work then try to bond with your colleagues.
Lastly, university is but a mere stepping stone into the real world. Embrace adulthood and get your self out there, you should find it easier to make friends now that you have matured and gained confidence.