I'd just share the wisdom shared by experienced pipe smokers I've met (including a few here): Smoke what you like, and like what you smoke. :D
Assuming your son has observed your own preferences and pipe smoking rituals, he probably has an idea of which blends might appeal to him based on their aromas, right? I'd encourage him to try one or two or three blends that produce the scents he likes, for starters. If he's drawn to aros, fine: He'll like or dislike them, and if he's inclined to stick with a pipe, he'll probably branch out and try new blends as you coach him along.
Though I definitely appreciate the majority opinion here that you shouldn't start with an aro because of the likelihood of tongue burn, etc., I amicably disagree. :wink: Taste for pipe tobacco is as subjective and individual as anything else (preferences for food, wine, clothing, art, etc.). If your son thinks he might like to start out with an aro, offer him a couple of good-quality blends (I also thought of Lane's 1Q, LL-7, and Dan's Blue Note - as well as MacBaren's Vanilla Cream or Black Ambrosia, or maybe Stokkebye's Optimum). All produce a mild smoke and probably enough flavor for a novice to appreciate. And I've always found that it's easy to avoid tongue bite if you smoke a quality aro reasonably slowly and rhythmically.
When I started smoking a pipe in my teens, I wanted the aroma of my grandpa's signature blends, SWR and Amphora. I quickly figured out that Amphora produced a cooler smoke and that I could enjoy a smooth, even smoke by pacing myself. I never quite figured out how my grandpa could smoke SWR continuously throughout the day w/o constant tongue burn. He agreed that Amphora smoked cooler, but he thought it was less flavorful. For a noob like me, it was just right. I eventually branched out to other aros and then VAs and English blends, with encouragement from more seasoned guys. Considering what drew me to the pipe in the first place, I'm not sure I'd have stuck with it if I'd been steered toward stronger tobacco flavors so early.
The 18-y-o son of a good friend recently tried a pipe for the first time (never having smoked at all before) at the urging of a pal who'd been smoking Captain Black. Predictably, both guys say they love the sweetish scent of CB in the pouch and the smooth aroma of the smoke, but they don't get much taste and burn their tongues after one or two bowls. I gave them some 1Q and Optimum and then offered a couple of pointers on packing, lighting, and smoking their pipes. They were overpacking, smoking unevenly, and sometimes not even smoking a full bowl. Now they tell me the experience is totally "awesome" and have started sampling all kinds of new tobaccos (as well as building up modest pipe collections). A little encouragement to smoke quality tobac and learn good smoking technique can really make a difference when it comes to introducing new guys to the hobby.