7mm what?...7x57, 7mm Express (.280, a darn fine choice), 7mm-08, 7mm Remington Magnum (what you probably meant, but what should be your last choice), 7 mm Remington Ultra Mag, and 2-3 other magnums.
The first 3 are excellent choices and the others are not. The last ones are not good choices for somebody that doesn't shoot alot, they are "expert" calibers in that they kick like a mule and will dot your eye in a heart-beat. Don't get me wrong, they can really fling a hunk of lead a long ways and are pretty darn accurate....BUT< BUT <BUT
For somebody that does a heap of shooting, they work just fine...but here is what will happen...you'll go to the range and he'll immediately notice that it kicks and after the things cuts his forehead he will never be able to shoot it accurately again...I guar-an-darn-T-it.
Get him a .270, 280, 7mm-08, 7x57 (7mm Mauser) or .260, 25-06, 30-06 .308 or even a .243 (the first four are my choices and the rest are not necessarily in order) get him to shoot so that he can hit a paper plate at 50, then 100, then 200 yards. Even though he is an adult, the "entry level" process is still the same.
I have a .270 and an '06 and those are both excellent choices in the bargain rifles, but my caliber choices are listed.
Please don't get him a magnum.