While most colleges technically do not require calculus in high school, opting out of calculus after finishing precalculus before 12th grade can look bad to an admission reader at a more selective college, and can be disadvantageous in college if the student’s major requires calculus.
As a CS major in college, he will have to take calculus for his major. AP calculus AB will be a slower gentler introduction to calculus than calculus in college will be. Better to take calculus in high school after finishing precalculus in 10th grade rather than skip math for two years and then take full speed calculus in the first semester of college.
http://math.buffalo.edu/rur/rurci3.cgi may help him determine what precalculus concepts he should review before taking calculus.