I think you can get a rough idea of age using scales, but it's open to some amount of interpretation. Otoliths are the preferred method.

Here: http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=308826

"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.