Meh, best time to start the BIS counter is at birth, second best time is right now. Agreed with WineCountry the marginal returns are small until 25k-ish BIS a year, but hey, I didn't set up Continental/United accounts until my early 20s, and I can only imagine how much closer I'd be to MM if those first decades of flights had been counted.

Both of my kids had MileagePlus and email accounts before they went home from the hospital when they were born.

My point - just let the miles accrue, and have him fly whatever he flys.