Hip angle depends on belly fat and breathing. Big Mig used less hip angle than most because he could breathe better and so his speed on the flat was higher that way. That's pretty common and doesn't have much to do with age. Belly fat has to do with age. It gets harder to keep it off as the years go by. But there's no intrinsic reason why an older person can't use the same fit with which they were faster as a young person.

I was always a self-fitter, but a couple years ago I developed a saddle sore and thought what the heck, why not try a pro fit. I went to best fitter in Seattle, who changed my fit slightly: 3 cm less reach, ~2 cm up. I gotta say, I'm absolutely no faster or more comfortable, but I've spent about $600 on the fit and equipment changes he recommended, and I'm no worse either, so I'll keep this new fit. My old fit had a slammed -17° stem and the usual bars of 25 years ago. My new fit has a slammed -7° stem and compact bars. Eh. I'm probably a tiny bit slower on the flat, but I don't care, my power is off anyway, so I just draft more, and I still beat everyone on the descents, so it's fine. Saddle sore is still with me, the fit didn't help at all. And 200k feels about the same either way. I'm just as flexible at 74 as I was at 25 and I squat almost the same. The saddle sore, just one one side, seems to be some hip alignment issue that no one can detect or offer a fix. I measure exactly the same both sides, one legged whatevers are the same both sides, Eh.

If my thighs hit my belly, that's a good reminder to eat a little less. It's all good.