I'm so late to watching this lol but Walker is of course 17 but he just turned 17 in January. He was actually 15 while filming most of s2 and Leah was 14 turning 15 filming s2. So in actuality they were only like 1-2 years older than what they were supposed to be. Also 13 year olds these days especially boys tend to look a lot older than that and when I say that I mean some boys look 16 but are like 13 but of course they are still babies.