I don't believe most people list "age" as a reason to get married or not get married once they are of legal age to make their own choices. "Life is a personal journey".
We don't get to pick the spouse of our loved ones in our society.
Naturally most parents would not want their 20 year old to marry a 50 year for numerous reasons but I don't know if we can honestly say it's "wrong". There are no laws established to limit the age disparity for (two adults) to date or marry whomever they choose. From the stand point of "right or wrong" all we can do is state why it's wrong for (us) or why we wouldn't do it.
The other thing is to point out possible challenges the couple may have to deal with which they may or may not have considered. (50 and 20 is a lot different from 80 and 50...etc)Having children who may or may not get to spend much time with the elder parent.
We see people like Michael Douglas who is 25 years older than his wife Catherine Zeta Jones and they seem to be doing fine.
On the other end we have Hugh Hefner who is 84 about to marry a woman who is 24.
Does society view the age difference differently when the older person is a multi-millionaire or world famous???
(Larry King, Clint Eastwood,Tony Randall...etc)
It also happens the other way around Joan Collins is 32 years older than her husband Percy Gibson
Obviously health issues could be a major concern as well as the younger person may be making a choice without the benefit of being mature. Thankfully divorce does exist for couples allowing them to walk away from marriage mistakes.