A therapist will only have a personal opinion which to be honest they're not really allowed to share - therapy is about reserving judgment and working on a persons difficulties regardless of whether a situation is 'right' or 'wrong.'

Is there anything inherently wrong about a man of that age dating a 20 year old? Well no, i mean they're of the legal age of consent, they're old enough to be responsible for their own decisions - though how much is something that usually gets better with experience.

My concerns would be focused more on the level of compatability - what would you have in common? What are the shared interests? What are their long term expectations? I think as long as you're realistic about your own expectations and respectful of theirs i don't really see the harm. 20 years olds aren't stupid - not enough credit is given to young adults in my view. They have a responsibility for their actions just as much as you do. It's not always a case of daddy issues or a want for a sugar daddy. Younger people are capable of sincerity.

I hope this is vageuly helpful. Good luck.