As you get older, even getting out of bed gets harder, but a 50/1.4 is going to be more iffy than focusing a 50/2 for anybody, no matter how good your vision is. I admit I am not understanding why, short of macular degeneration, age would have much if anything to do with it. I'm 67 and wear trifocals; I have difficulty with exposure, composition, and remembering what film is in what body, but I don't have any more difficulty with focusing than I did when I was 16.
With corrective lenses, vision can be corrected, in most people, to 20/20; astigmatism can be corrected usually as well.
20/20 is 20/20 is 20/20, no matter how old you are. The only reason one would be unable to focus as well as when they were 20, once they got to 50, 60, 70 or whatever, is that their vision is not corrected as well as it could be.
It is only if your vision can't be corrected to 20/20 for some reason that age should enter into it. Even then, that is an individual problem, and not an age problem per se.