Never felt lonely once in my entire life until I graduated from college, got a full time job, and moved out of my parents house. When you're constantly surrounded by people your own age for at least 40 hours a week from elementary school through college, and then suddenly you aren't anymore, it feels like a punch in the gut (at least it did for me). It's way harder to build relationships with people you don't (and can't) spend even close to that much time with anymore.
For example, you meet someone in passing, out shopping, at a football game, whatever......you have approximately the length of that interaction to make a connection, or you will probably never see them again. Doesn't matter if you're trying to be friends with someone or trying to date them. It's harsh, and I wish it was something someone told me. First impressions turn into only impressions when you get older, unfortunately.
If you're a naturally social person, then you'll probably be ok regardless, but if you aren't, meeting people only gets harder (way harder) as you get older.
