I don't mind Billy aging. It's called "progression". So, unless you want Billy and company to become "magical creatures", as seen in that one scene in Darwyn Cooke's NEW FRONTIER, then Billy has to grow up. Otherwise, you'll risk getting a "Claudia" (THE VAMPIRE CHRONICLES) or Miracle Boy (MIRACLE MAN) situation.
https://ufonaut.tumblr.com/post/7090...t-you-and-your
At least, YOUNG JUSTICE, the animation series, did it right...
Though older, Billy is still enthusiastic and youthful, not at all dissimilar to how the live actors (Frank Coghlan, Jr. and Michael Gray respectively) played the character. I think that too many of us fans want to put the character(s) in amber, due to many reason, including how we think his potential was robbed when the characters were literally taken off the market for a number of years, and then brought out to be played for laughs. And, personally, I never really bought into the "Billy has to have a pure soul" trope, which makes him the Virgin Mary of comics. I prefer the idea of Billy having a noble soul, and striving to do the right thing, with the guidance of the Wizard.
I just hope that Waid's treatment strikes a nice balance that everyone can be supportive of.