Not sure I agree with that.
Genetics determines when your hair starts to die and fall out. Not whether it will or not, except in very rare cases of full-head thickness into old age.
Cutler and Wolf are the best examples. Full heads of thick hair through years of juicing until the hair started to fall out and not grow back. Now they're Bosley brochure in 5 years.
Both my grandparents (esp one from mothers side, which is most important allegedly) have full head of hair. The one with better hair died at 73 with a thick bush on his head. And if you are prone to MPB - steroids WILL accelarate that "when" a lot. Of you are not - you may be 100 and still with the same hair.
That reasoning is similar to some peoples reasoning on getting fat. They always say me "Don't be too happy, with age you'll start accumulate fat too.. look at me, I was lean when young.". Yeah, right... fatness is NOT in my family genes and every single person, regardless of age/lifestyle/eating habits is slim/was slim till the last breath. It's GENES what's most important, not anything else.