Two adult humans can do as they please free from judgment as far as I'm concerned. Once you've checked someone a) is an adult with capacity and b) consents, everything else is subjective fuckaboutery and opinions based on misguided feeling of what 'seems right according to society. Nobody's business. Wasn't anyone's business when Leonardo Di Caprio split up with yet another 25 year old, also not anyone's business if Cher starts dating someone half her age. Over the age of 18? Consent to your relationship with the other person/people? We're all good to go, no further questions. :o)