A more likely scenerio is that heavy usage inhibits critical thinking i.e. learning at any age. Much of the knowledge and reasoning powers held by adults are processes built on information acquired in ones' youth.

Pot may not cause adults to forget, but it may make it impossible to remember what they never learned.

*shrug* The persistent use of a lot of substances will give you brain damage. Alcohol does the same.

And in other shocking news, donuts make you fat.

OP clearly had a fun childhood.

That's permanently, OP.

Impacted you perhaps?

ndividuals who smoked heavily in adolescence had consistently lower IQs at age 38, even if they'd cut back in the previous year. By contrast, the IQ of the relative latecomers to marijuana was more closely linked with how much pot they'd smoked recently.
"The effect of persistent cannabis use on intellectual functioning is really confined to adolescents, (which) suggests that adolescents, in particular, are vulnerable to the effect of cannabis," says lead author Madeline H. Meier, a psychologist and postdoctoral researcher at Duke University in Durham, North Carolina.

http://www.cnn.com/2012/08/27/health/health-teen-pot/index.html?hpt=hp_c2