He will need at least two A levels and then do a degree in Sports and Physical Education or Sports Science - this will take three years.
Then he will need to study for a PGCE - one year - which will give him qualified teacher status.
The University of Bedford does it as an 'all in one' 4 year course - their entry requirements are here:
http://www.beds.ac.uk/courses/bysubject/spoexe /ba-phyedusec-bc
As you can see, they are asking for two A levels and 5 good GCSEs, including English and Maths.
Hope he is still keen when he's read that. :)