You go, man! I hope mine gets like that. I want it to look like I have AA batteries in my arm, and people point and stare.
But seriously, bigger is better. Aneurysms come from repeatedly sticking the same close area but not actually making buttonholes. The tissue gets weaker and weaker until it balloons up. Doesn't sound like you're doing that. And the fact you're young and active means you've got a fat healthy fistula that will last a long time.