Yeah, Ra's has gray temples in BB and the comics and animated versions. And in the Batman Beyond episode, after elderly Bruce takes a dip in the pit, he has a full head of hair...with gray temples. But I don't think it's necessarily suggestive of him taking a dip in this case, I have a feeling his temples are gray in the movie before he even encounters Bane. Bruce turns 30 in Batman Begins, Joker mentions that TDK is a year after that, and we now know that TDKR is eight years after TDK, so Bruce is 39 or 40. It's not uncommon for a man that age to start going gray, especially if he's under a lot of stress.
In fact, initially assumed the gray temples were just makeup for the character, until I saw some recent CNN footage of Christian Bale in China. Unless he just hasn't rinsed it out since filming ended, or is sporting the gray for another role, the dude is already graying...and in real life, he's 37.
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