I agree with the others who said good on you for handing down your gear.
My new skis are six years. They don't ski as well as my 14 year old Elans, so if you want real improvement I guess you need to get something more recent than 2004s. When did they start making the good skis?
I ski pretty good on bad skis, your son should be fine on those K2s. Bode Miller revolutionized ski technique on the similar but stffer K2 Fours. If your son needs to ski better than Bode did in 1998, he will need newer, better skis.