As a few have already said, its the maturity of the driver that matters, he/she should know not to push the car more than they can control.
Im only 19 and the first car i learnt on was an 86 telstar, by the time i hit 17 i was driving mate's 180's and skylines and learnt slowly how to handle something alot more powerful.
When 18, i bought my 180SX and drove that without any problems (and as two40 knows, i enjoy alot of sideways action).
Now i work for a company that imports alot of skylines, including big horsepower GTR's, ive had the privelage of driving some of these cars, and havnt even scrathed one of em.
If this is his first powerful car that he will drive, and is quite the dare devil, then go to a few track days and driving courses so he can be more confident in controlling a car such as a skyline.
But if he is a smart chap and wont do anything he knows he cant control, then go for it, and learn slowly.
cheers