Happy Birthday, the gift I'm going to give you can't be bought, because it's knowledge.
There's still a long road until you turn into an adult, and you must be ready to it's responsibilities once it comes, but not yet.
Youth's energy is unique, because once you turn into adult you cannot have the amount of energy you had at this age anymore. And you must know how to use that energy wisely, that energy is both mind and body.
Once that energy disappears, it will never come back with the same equality, just like the time doesn't. Energy and time are limited things, remember that.
Happiness can be obtained by being satisfied of yourself, and only you decide to not be happy. Nothing is needed to obtain it, only your mind decides that.