Simple answer is cannabis has too be mature. If you pull your plants early you wont get a high.That said we wont know what strain he was growing if it was mainly a sativa you need 12 too 16 weeks depending on the strain so if he pulled his plant early no buzz.
Trichs do have to change colour milky/cloudy ,aldo again depend ing on the strain Indicas when left late should be more couchlock were as a sativa left longer should get you higer less racy of a buzz. Medical use depends on what illiness and the person.If you looking for pain killer smoke Indicas....It really depends on the person for eg some depessives can use Sativas but if you find urself being overly para perhaps Sativas are'nt for you...
In short the only way too properly grow is let let them finish according tooo the breeders who growen it many more times than most of us will get the chance too.

Drought