I agree. The age gap is really the problem (and the reproduction thing doesn't help either). If you made the Ocampans like all the other Star Trek humanoids, or did the time travel thing or whatever, then no harm no foul.Yes. Under those circumstances, either Tom or Neelix would be a worthy match for her.
But, then, of course, you pretty much would take away the very unique element that is the basis for the Kes character to begin with.
The character was perhaps the franchise's worst conceived character to begin with and that was unfortunate for Ms. Lien. She was saddled with something that was hard to work with from the very beginning. I think she did the best she could with what she had.