I started uni at 20 and also stayed at home, I just finished my first year and didn't feel like I missed out on the university experience at all. I managed to make loads of friends, and actually made sure they were real friendships rather than just being friends with someone because you're forced to live with them, or just bickering because you see them so often. I went to a lot of the freshers events during the day which meant I met people when they were sober rather than becoming drunk bffs with people on nights out. My uni also had an event for local students/stay at home students to meet one another prior to freshers week.
I met my closest friends on facebook during the summer before uni started though. There was a facebook freshers group and I met a few course mates on there, they've been my best friends ever since.
You'll find a lot of people will say they feel sorry for you not being in halls and missing out on the uni lifestyle, but when you're actually there, a lot of people will wish they were in your shoes. Able to go home and sleep in their own bed and eat real food. Not having to put up with hundreds of loud students when you're trying to sleep or study, not having to put up with 7 other people's kitchen mess etc. There are no cons to living at home, in my eyes. Plus, I've managed to save a huge chunk of the amount I'm trying to save for a deposit. I couldn't have done that in halls.