Sorry didn't realize you were 15 - I guess I sounded like the Mom I am...

Listen even though you are young, never too late to learn there's a right way to ride... I would bet there are skills classes in your area and some may even be free.

For rock/log hopping or curb jumping, you just can't ride full speed and ram the obstacle hopping the bike will go up and over... you have to weight yourself off the front tire, pulled up on the handlebars and lift the wheel up (think of a rearing horse). Once you get the wheel going up it should continue up over the curb. Practice first on something smaller. For instance a driveway where the curb will dip and then get bigger. Start at the easiest height and then build up once you master the wheel lift.

Like i said, mountain biking is all about skill - its just not ridng hard and hoping for the best. And a young man should never ride without a helmet - just too young to start building on all those concussions. I can't tell you how many of my friends have permanent brain injuries (including myself) take care of yourself - don't make your future life any worse than it can be.

Go to the library or a book store and look up books that offer mountain bike skills. Essential skills are climbing, decending, weighting off the front and back tire, and falling. Boy knowing how to fall properly has really saved my head and limbs!