So basically I am almost 16 years old and looking for something fun to do on weekends. I have always thought about a dirt bike or go kart. I don't really know how much horsepower my first dirtbike should have or what kind would best suit me. I also was wondering where exactly I could ride. By the way I am about 6 foot and 145 lbs. Thanks for any help you can give me.
If going much distance, you will need a trailer for either a Kart or Bike, but if you need to, a bike can be pushed around the block, a Kart would be more work in that sort of case.
Karts are probably less likely to break bones etc, but are much more restrictive on where you can use them.
As for where to ride, in either case, start with a Google for dirt bike or go kart clubs in your suburb/location.