Yes, it's probably a preflop fold and you probably shouldn't even have a calling range if villain 3bet less than 5% with that size. Just 4bet your QQ+, AK and some KQs and AQs.

calling seems alright, AJs has good equity, but I wont be calling much worse than this. If that is a fish and low sample we can still realize our equity and make our call better than folding. It is not like we calling 98s which has less equity overall and vs big size should be folded.
postflop plays itself

A sample size of 21 hands isn't sufficient to get a sense of villain's real 3bet %. However, the fact that he has a PFR of 0 over those hands tells me that he's not comfortable raising preflop at all, which makes the 3bet pretty scary. A FPR of 0 also tells me that villain is a weak player. Based on the limited information we have on him I would just fold, although calling is certainly not terrible. It's just that your hand does poorly against what is probably a value heavy 3 betting range. Turning AJs into 4bet bluff might make sense in other situations but versus the general player pool at 5NL it probably isn't advisable.

The turn is an easy call. Setting aside his bluffs you rightly pointed out that he can have AK or AQ. He could even be taking a funny line with KK, QQ, TT (we have already established that he's a weak player). If he turns over a monster it is what it is. We just need to beat one third of the hands he can have to make this call profitable and we're doing A LOT better than that.

So preflop I would not be upset to see a fold here. Very small sample size so we're really not sure how aggressive this guy is going to be with his button raises, but remember he knows that he's raising an UTG open. Since we don't have too significant of a read here we should use a much more general strategy. So we're gonna want to 4bet for value with our best hands TT/JJ+, AK, we're gonna want to fold our worst hands (of which this hand may fall into), and decide whether or not we have a calling range while we balance our 4betting range with a few bluffs. There are a few problems with having a flatting range in this spot. Firstly we are up against a fairly new opponent. 21 hands is not a lot and we don't know how he's going to treat the situation post flop. If we're calling with the plan of giving up if we don't connect with the flop then the flat is really not appealing. We're only going to connect with the flop 1/3 times, which means we are getting direct odds for that draw. However, we are at a range disadvantage for a lot of the flops that we do connect with. If we hit a jack then we still lose to JJ+, all of which are in our opponents range and virtually none of which are in ours. Because we're getting direct odds for the draw, it's also understood that when we do connect, we need to get more money out of him in order to be profitable. If an ace flops and he has QQ, he may literally just check/fold flop. That's before we mention that BTN could be 3betting for value with all AQ and AK, which is a lot of hands that have us hurting bad on an A high flop.

That is a big write-up all to say that flatting AJs here against a new opponent is a dicey situation at best. 4bet or fold. I recommend folding because 4bet bluffing here is something we need to be really sharp about and I'd probably do it with a hand like AQ or A5s. I'd love to have a hand like 86s in there too but then you get into spots where you may just be 4betting too much and we're not really happy there.

I like not ever having a raising range on the flop. We don't really have AA or JJ pretty much ever so a raise is repping 77 or AJ, that we can maybe balance with a hand like T9s or 98s with a BDFD. Because we're letting go a good amount of Ax and 4betting some Ax, he knows he's got a range advantage when that ace hits so a bet probably comes with a good amount of hands that don't have aces in them so we're likely calling with a few speculative hands and trapping with strong ones. Like if he has AK which is perfectly likely, it will be very easy to have him all in by or before the river, and with top 2 I am loving that situation. If he has QQ then I don't want to be putting him in a tough spot. Love the flop flat call.

Turn, nothing has changed. You are so far ahead of his range it is mindblowing. Sure, he has AA or JJ sometimes, but guess what, we block both of those hands. And yeah blockers in HE aren't always super worth talking about but when your hand limits your opponent from having 6 strong value hands to 2, that is a significant change. Call his turn shove or I will find you and set you on fire.