Not everyone on this forum is in the Uk for one. Secondly, age gap alone is not the issue, if you have two developed adults, (like the poster who gave his parents as an example)
However, if she is 18, a 31 year old man in my view has no business being with someone theyve had their "eye on" since she was 16. He didnt break any laws by marrying her (if 18) or whatever the legal age is in that country, However that doesnt make it less weird or disgusting for me personally.
The other given example is some actor or whatever at 50 marrying a 18 year old, totally legal but for me repulsive.