You can say the same thing about girls- whats the difference between an 18 yr old girl and a 21 year old girl? Trust me most 21 yr olds are more mature…I dont think it has to do with what you do. People mature gradually and at some point they can see that they are way more mature than they were 3 years ago.
Whats the purpose of this anyways? Are you saying you want to date 20 year old boys?