How do you find older men?

As an 18 year I started to realize I don’t like the guys my age mostly because they’re immature. However, the problem is I don’t know where the hell I would find someone who’s older in their late 20s to early 40s. Like I can’t just randomly start flirting with a grown man as an 18 year old girl. Anyways I just need to know where to look.