A person at age 40 (or 30 or any age) isn’t suddenly considered to be younger by anyone just because they’re infertile, in my experience. But heck, I don’t know; with all the anti-aging research going on, maybe we will be successful at ending age-related mortality in the next couple of centuries, and “old” would literally become just a truly relative number. For the time being, all I can say is that in my family and circles, about 35+ is considered not-young for any human, and especially 40+.