Why is it easier for me to make friends with people in their late 20’s and older compared to my age group?

I (19m) notice I have an easier time making friends with people older than me compared to people my age. For example, if I ask my lab partner or a classmate that I sit next to out to lunch after we're halfway through the semester, I'll get a "mabey" or a "sure" and no follow up. Yet I can go to a gaming bar, and the second time I go there I get invited to their pilgrimage that they go on around every two months to an arcade 140 miles away. While it's easier for me to make friends with older people, I also want a group of friends my age because I could better relate to them.