It sounds like your son is pretty knowledgeable about hair so that's a good thing. He may want to try hair pomades to control the frizz. Gel also helps but may not give him his desired look, as his hair may be elongated on the first day or two. Also, I would highly recommend he consider co-washing some days given the amount he washes his hair. That will better help him retain moisture which may help with curl definition as well. I should also say that maybe he doesn't have a lot of curl definition. That's largely determined by genetics and can't be helped much. Personally, I don't have much (mine is more loosely coiled) but gel and curl creams have really been my saving grace. HTH!
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Favorite products:
Shampoo: KC Come Clean
Conditioner: Tresemme Naturals
Styling: Donna Marie Dream Curling Cream, EcoStyler Gel (pink)