Responses
I don't remember reading how big the age gap is, but Josh made it a condition that he wanted to wait with a second child until after they were married.
If I have to guess he was most likely conceived on their honeymoon.
So Cecil is younger than Spence.
Pete in KMIYC main story is probably between 2 and 3 years old. I guess that Cecil ~3-4 years younger than Pete.
Both are probably so tall because of the Miller genes, the male alpha miller are all past 2m tall, with Chase being the smallest I think.
Novel readers, what's the age gap between Pete and Cecil? Seeing them in Kiss Me Liar, I really thought they were twins