I have found that about 200mg of caffeine can induce hypomania for me. The dose at which tolerance develops varies between individuals but on average is about 400mg per day. An eight ounce cup of coffee is about 100mg. Adolescents and children have different needs which should be taken under consideration, one of which is developing an addictive habit.

Caffeine Addiction is No Joke for Some | Psych Central News

Caffeine addiction - Wikipedia, the free encyclopedia

Caffeine withdrawal is unpleasant, and that is one reason why individuals who have developed a tolerance to caffeine require a cup in the morning to feel alert. It can take up to two weeks for withdrawal symptoms to pass. I'd recommend speaking about this with a psychiatrist.