Is it okay to be flirting with a 21 year old but i'm 17?

Anonymous
Basically, a guy that I knew of once, has recently started talking to me, at first it was just friendly but now it's quite flirty and i'm also starting to like him more as we grow closer and he is quite obvious that he is showing interest in me too. The thing is, i'm 17 and he's 21. I am very mature for my age and I am often told that by others and he is a decent guy with a good job, ambitions etc. I also find that guys my age are too immature for relationships. I'm unsure though as to whether a 4 year age gap is too much since I am 17 so I don't know whether I should try and refrain myself from starting to like him whilst it's still in early days or not.
Opinions on a 21 year old dating a 17 year old girl please.
Updates
+1 y
legal age is 16 in my country by the way
Is it okay to be flirting with a 21 year old but i'm 17?
9 Opinion