I’m not sure age has as much to do with quality erections as general health and weight do.
I went through a phase where I dated older guys, usually between 40-55 and I usually dated professionals who were successful and in great health. I never noticed any difference in the over fifty guys, except their extra experience and their emotional maturity, which is what attracted me in the first place.
I try not to stereotype anyone and I think weak erections can occur in any age group that is not generally healthy and in a normal weight range.