It's an interesting one - I'm an old fashioned liberal, so if two adults want to exchange sex for money, or the promise of sex for money, or sex for no money, or lots of money for no sex - that's entirely up to them... because basically everything else is just subjective whataboutery.
It's not for me either but if other people want to go ahead and do it, that's up to them. Feminism is about the right to choose and some women want to choose this way of earning money. Fine. We can't start applying our own codes of immorality over the top of the law just because we personally disagree with it.
If we think sugar-daddy and sugar-baby relationships are morally reprehenisible and we can change the law to reflect that - a maximum of 10 year age gap otherwise the relationship is illegal - or raise the age of consent to 25... then we can start making judgments. Until that point, the law is very black and white and we're simply attemping to insert our own subjective standards.
Is he over 18? Is she over 18? Yes? Everything else is none of society's business - and simply results in a judgmental mess. But..but.. but he's 98 and her grandad's friend from Golf and she's only just turned 20. See question one. Adults are adults, leave them be.