Listen. Take it from an unmarried girl getting older in age.
If she has found someone, provided they’re not having sex, let them hang out. Meet the guy. Make it clear that you’d like for him to follow this up with marriage, and given it is 3 years, ask the guy directly what he thinks about marrying her within the next two years? Get the girl engaged now, if this boy is serious about it.
Nothing bad with nabbing a good kid early on.
Why do you think she shouldn’t be in a relationship, apart from her age? Is she immature? Do you fear that she’s having sex at this point? Do you think the guy is taking advantage of her? Do you think he’s not serious? Do you think he’s a loser, a moocher, a beqaar aadmi of sorts? Too old for her?
If there isn’t any issue, I’d introduce him to the family.