17 & 21... Too much of an age difference at this time?

Izzy • Love my horse, trying to get in shape again, taking life a day at a time 🤙🏻
I've been talking to this guy, I'm 17 and a half and he's 21 and a half, almost exactly 4 years apart. Would it be okay if we dated? He seems awesome but I'm just a little leery about the age difference. Would it be illegal? Or just if we had sex? Is it normal for an older guy to want a senior in high school? I want to go for it but if there will be problems I don't want to get my hopes up.... Some advice please!!