I've just been best man for my friend, who just married his first girlfriend at 41.
There's nothing wrong with him, he's an average looking guy, a bit quiet and geeky, but not to the extent that he can't hold a conversation.
He just never seemed that interested in dating. Pulled a few times in nightclubs in his 20s, met a few women over the years and had a couple of dates that fizzled out, more from his side than theirs. He had a social life, was happy living alone, just didn't seem to need a relationship.
Then suddenly at 38 he announced he was joining Bumble. Had a few dates with different women and then one of them stuck.
Him and his wife seem very happy together, and I don't really know what changed for him, but he's a good man and I'm sure they'll have a good life together.
I'd say it's certainly a red flag if someone hasn't had a relationship at that age, but it doesn't mean he's definately a wrong'un