OP - really there isn't much you can say to the person you speak of. We were all young once and probably not well-eared when it came to advice reception. Encourage him to shoot and when he does less well than he hopes don't be overly mocking 
DSR 50 is $25,000 then after taxes, optics and other odds and ends you can hit the $35,000 pretty easySo what does a $35,000 sniper rifle look like?
Pricey. I wonder if the DSR1 is still in the $10 000.00 range?
You say nothing. You take them out to shoot. When they can't hit a target at 1500 yards, you look at them like they're stupid and ask them what's wrong.....them proceed to laugh maniacally. Maybe they'll give up on shooting when they figure out its not that easy and you'll have a chance to buy a really sweet gun for cheap!
best suggestion so far.Pavmentsurfer, let him save up and buy a sako trg 22, used, if he fails he can sell it and not lose a dime. Regardless of what people say here, more uberly accurate shooters, are gifted from birth, they are steady, and their eyes and anticipation work much better than the masses. You will only know by trying. I have seen a 6 year old kid hold 1/2 moa out to 200 yards with only a bipod, no rear rest, and only get better with time. I don't think any discouragement is warranted. Guide the enthusiasm, dont tamper it. a TRG with good factory ammo, will fill the need, and not cost a thing but ammo. good luck and enjoy your time together. Whatever you do make sure you put a shooter in his hands so as to eliminate the equipment being at fault.