Jetamio;87003
That's like taller than me in rl, thats one huge kid. As for weight, I have trouble converting it into stones, but it would have to be someone with a decent weight about them to carry another into the air lock thing. It would also require strength or sheer size/weight to hold down someone thrashing under a pillow.
He's tall, but skinny... 125 pounds for someone who's 5'6 is quite underweight.
Regarding the method of the kill: I imagine it's not extremely hard to keep a pillow on someone's face if you're on top, all you need to do is keep your weight on them. They would have to essentially benchpress an entire person in order for them to get it off...