I'm quite a few years older than you, but I also find it difficult to be friends with people with jobs and busy, "regular" lives. Unless I do meet them through some sort of group (like singing or volunteering) I feel like we don't have much to talk about.

I go to a therapy group that meets weekly where most of the member have both mental health and physical health issues. This group is helpful to me. I haven't made close friends there, but it's good to hear from other people who have life situations similar to mine.

I hope that you find something to help you with your loneliness. Do you like animals? Having a pet/companion animal is helpful to me.