Just assumptions here, but it might also be a bit of self protection.

Yes, now he wants to be with her, but 24 and 42 are very different points in life. At 24 you have ambitions, at 42 you are settled.

So if OP lets it unfold and they have a relationship there will always be the question of how long it will last until those generational differences might collide.

Now of course you never have any safety that a relationship will last, but with this age gap it is more likely that at some point there will be insurmountable differences.

Maybe they even expect very different things from a relationship.

Again many assumptions, but maybe something to think about.