My sons hair always smells dirty

Hi! My son is only recently 9, but from about the age of 3 his hair always smells dirty. It will smell clean immediately after washing, but within an hour it smells like it hasn’t been washed in days. It doesn’t look greasy even though he has dark brown hair. It just smells greasy. It’s definitely hereditary from my husband/his dad. This is also an issue he has, even though he no longer has hair. Even his bald head smells like dirty hair. All the men in my husband’s family have gone bald. Even though I know that is most likely in the cards for my son regardless….I wonder if I can try to help or even fully fix this issue…he might be able yo keep his hair longer. My husband started losing his at only 28. Any recommendations on things which have worked for you or people you know with this issue? Things we have tried which haven’t worked: Dandruff shampoos Clarifying shampoos Tea tree oil shampoos Baby shampoos Thank you!