Thats solid. But as a 21 year old, I can tell you its much more difficult to build credit in the first place than it is to maintain. Got to play the game at some point or you wont be qualified to get a car/ home loan when you need it
Also, I'm pretty sure your credit score takes a penalty if you have no credit cards (or too many)
Appreciate the compliment but I'm only 29, meaning I stopped using it when I was 23, and only had 1 card with a $1000 limit and paid it off monthly when I did use it. There are fairly easy ways to get things like cell phone bills and the like reported to build "credit" without playing the credit card game, they're just not profitable for the credit industry and thus not very well known.