My eldest is five and a half, and has just got into ABC3 (none of the movies you've mentioned have cropped up yet, but my gut is that while he'd like the TMNT, the others might be a tad too advanced for him at this stage). Overnight he's gone from thinking Fireman Sam is the bees knees to absolutely loving Iron Man, Wolverine and the Super Hero Squad. It doesn't worry me, but I've found myself giving him reminders now and then that they are only characters on the TV and in stories (ie. they aren't real) ... lest he decides to put on a superhero suit and try to fly out of the tallest tree he can find.

I think it is dependent on the child, but I'd think they'd have to be school age before tackling some of the movies you've suggested, if for no other reason than some of the storylines are a bit convoluted (well, I found the latter Star Wars trilogy totally convoluted).