@Ryder96 rule of thumb if an elf asks you to guess, lie. If you can't do that, use human standards. Unless they're self-conscious about how young they look (rip the eternal Loli) it's flattering to guess younger.
Thing is that I could see Fooly really appreciating the sword, if given with story. Would probably end up a prominently displayed mantelpiece in his home, after he stopped lugging the damn thing around from his excitement.
Actually I don't think her first idea was all that bad. Fooly would have loved it for sure, and I could even see treasuring it. Something that well loved would be really valuable to her, so it's a sign of trust.