Is the age difference too high for us to date?

He's 21 and I'm 16. That's only 5 years, which isn't much older than the largest age difference that I've ever had in a relationship. I'm actually awkwardly mature for my age. Like, it's so bad that I even have trouble making friends because my maturity level is so much higher than their. But I was raised in a huge family, and from early on I've been hit with abandonment, death, financial problems, etc. Things like that really do age you quicker than others. So I was thinking, would it be so bad for this guy and I to date? It's not illegal in my state.