Ken Doctor considers new research from comScore looking at how and where we use our thumbs when performing tasks on our smartphones. Thumb-heavy users, as opposed to two-handers, skew young — 18-34-years-old. And it’s not just youth behind their thumb dexterity, but practice: the young tend to spend 3.2 hours a day on their mobiles, while 46-65-year-olds spend (only!) 1.5 hours.