They say age is but a number, but I think it does matter in the examples put forward like a 15 yr old dating a 25yr old, no way, but a 30 yr old and 45 yr old is ok, there comes a time in life where maturity hits, and the age difference does not seem to matter, but it depends on each individual, their personality and maturity, I feel.
I was once dating a man 13 yrs my senior but I was 30 at the time, and it did not make much difference to our relationship,except because he was older, he thought he knew better, hence we did not stay together, however he was an american with spanish background, so kinda victorian in his ways, so perhaps it was not the age thing at all, just his up-bringing.

I do find it hard to see what a 40 yr old could possibly find attractive in an 80 yr old myself!