i remember when i was 12 or so,i lifted with the ole 3 days a week/whole body workout till i was 15 or so.once i joined diamond gym i started watching and learning about more advanced type of training methods, i switched to a 3 on and 1 off,
pecs-tris-monday
back-bis-tuesday
legs-delts-wed
off-rest day-thur
repeat mondays workout on friday and so on. it worked great and stayed with that for 2 years or so,then i started experimenting with training 1 bodypart a day and training 5 days in a row before taking a rest day. im a huge believer in the more advanced and bigger a person gets the less he should train and the more he should rest, when he does train its short,brutal and intense though.when a person starts out lifting they will grow pretty much on any routine cause their bodys aint used to the stress on the muscles and will get bigger and stronger regardless,as u get bigger and stronger u must adjust your workouts or else a person will hit a sticking point