Make an estimation of your opponent's range. Always.
How nitty is nitty?
Pre-flop most of that range is ahead of AJ.
12 hands are 50/50.
15 hands are 70/30.
3 hands are 90/10.
24 hands are 75/25
42 hands are crushing your range. 12 hands are about even (although slight favorites against AJ).
So how many hands total is a nitty nit playing on that range?
Pocket pairs: 27.
Maybe throw in KQs (4), KJs (3).
Total hands: 54/70 hands are ahead. 42/70 are way ahead. You're out of position. There's nothing wrong with folding here!
I don't like 3-betting here because you are mostly folding out hands that you are ahead of! You fold another AJ, maybe AQ, 99, TT, POSSIBLY JJ. But otherwise you're folding A10, KJs. QQ, KK, AA, AK, and KQs are probably sticking around. So the only benefit here is that you have strictly narrowed your opponent's range.
Looking at it that way, you can see why RELATIVE value is so important. Playing AJ against a nit for me is that same as playing A4 (actually I might prefer A4s to AJo). You're not looking to hit top pair, you're looking to hit two-pair, a straight, a flush, or some kind of combo draw. It's not that you can't do it, it's just that you have to know what you're up against! 99-KK it's going to be hard to get paid well if an Ace hits. AK and AQ give you pretty bad reverse implied odds
if an Ace hits. In most scenarios you're looking for a controlled showdown.