I will be starting Uni this year at 28, I can fully empathise with you.
I've done an Access course over the past few years with other adults, and usually I have been one of the younger ones, but there have been a few 19/20 year old, and have felt as though I am a lot older than I am, which is a concern I have for when I start uni too.
I thinknits just important to focus on how you are doing something good for yourself despite any setbacks you have been through. For many students going to uni is just a linear path, school, college, uni.
For mature students it can be really hard throwing yourself back into education, so I think it's important to try to be proud of yourself, rather than comparing yourself to others.
Are you a member of any societies? Some unis have them specifically for mature students, and if not, maybe joining one that you are genuinely interested in will give you a chance to get to know other students and have fun focusing on something without constantly thinking about age if you're around like minded people