A 19 yo is legally an adult so there is nothing legally wrong in an adult male pursuing her, but except in rare cases, a 19 yo is not mature enough to make adult decisions, so when a man 10 or 20 years older has a predilection for girls that age, it’s either he likes immature...

...girls for their malleability, or it’s purely physical and he just like fresh young things, neither of which is very ideal re the man’s character, or re the effect on the young girls.

There are gray areas, different things that affect preferences for both the men and the 19 yo in question, but because it’s so easy for relationships of that nature to be predatory, it’s never going to look good.