Adult friends history ranges from grooming age

I just found out my group of friends met at 13-20yrs old.

I’m 28M and moved to a new state 4yrs ago. I met a group of friends that were my age or older, and I just found out that they have been friends for 14+yrs. Which means that when they met, the youngest was 13 and the oldest was 20.

Everyone is over 28 now and some are still friends. It’s fine now, everyone is grown and seemingly functional. But that felt like a grenade.

In high school, some friends and I decided that one of us was being groomed by a 21yr old she met online. It was honestly innocent, nothing sexual, but we helped her determine that them talking was wrong because of their mental state. 21yr olds can handle alcohol, even if he wasn’t pushing sex or alcohol on her, he was allowing her to get drunk/do drugs around him alone, so even if it felt like a safe place to be free, it was a bad idea to hang out with this guy.

If I were to find out today, 10yrs later, that she was back in contact with this guy, even though they’re both now legal and it was never sexual, I would be grossed out.

So why is it different with these new friends? I found out the youngest/oldest ages of when they met, and I’m not grossed out. But if my friend from high school was still friends with a guy from that age, it’s weird.

….what???? Am I the problem here??