I think anyone can as long as they are somewhat physically fit. It's not as hard as you think. You would have be extremely over weight and out of shape not to. I've pulled pos 6 g's and 3 neg g's. It's easy to grunt and tighten your stomach during positive g's but harder in negative. You're floating during one neg G and have little control of your body. You can still do aerobatics with minimum g's have a blast. One of the ladys in the vid sounded like she was having an orgasm and she was only pullling about 4 g's and 0 negs, lol. Anyway, I just saw today that a T-38 went down killing the pilot (captain in the service) and injuring a crew member...sad day. I would love to fly a T-38...wow. I like your job, you're a special man with a lot on your hands. Don't count yourself low, gutzglory goes good with your job.
EDIT: btw, the Asian guy in the video that was collapsing in his seat was pulling close to 6 g's and looks like he purposely wasn't tightening his stomach. I think this was put on just to show the affect of g's to impress people. I've seen videos of 500 mph Red Bull pilots pulling 9 g's and looking better than that.