As others have said, stick to the “standards” available over the counter - 30-06, 308, 270 and (gasp) 6.5 Creedmoor.
If he wants to get fancy later in life that’s up to him, but at least with any the above he’s set for life to hunt anything in NA.
Aside, whenever a guy new to Montana who would like to start hunting asks me what sort of rifle he should get, I tell them to buy a 270.