About 100 billion neurons (these are the brain cells conducting information). To give you an idea, a truck full of sand would contain about 1 billion grains. More important for intelligence are the connections between the neurons: Each of them can be connected to thousands of others! No computer can match that.
Maybe the number of neurons and connections changes through life, but I’m not sure how. At 13, your brain is still developing, so you could get more and more clever with time! Here’s a picture we took of a pig’s brain matter blown up 3,500 times. Lots of space between the neurons hey!