You should listen to your boy! Yes soil grown weed takes longer to mature, but like Cannaman already said, you will have a larger margin for error if something goes wrong in the soil. In hydro you can really fuck your shit up if your water pump dies or your ph meter is off or something like that. Plus, THEY SAY that weed grown in soil tastes better than weed grown in hydro so you will probably get a better tasting product in the soil. I would just listen to your boy until you get the hang of things, especially if you are depending on your crop for $$$.