Dang, 3.5' for a 10 month old is huge lol. My sunglow was 3.5' at like 1.5-2 years old. My 1 year old guy is about 30" and eating adult mice every week. But every snake is going to be a bit different but there will still be averages. My 3 year old sunglow girl is about 5' and my 4+ year old normal girl is 6-7' probably pushing towards the 7'.
I don't have weights for them except my big girl who at last vet visit weighed in a 12.7 lbs.
Basically it boils down to feed boas conservatively. I feed once week while they are on mice. Then once they graduate to weaned/small rats, they eat every 2 weeks. Then once they are up to medium to large rats, it's every 3-4 weeks. This is for my females. My male gets the same schedule but at medium to large rats, he will eat every 4 weeks.
And remember, anything 'jumbo' is probably not good as that usually means retired breeders which are usually high in fat content. Also boas should not eat guinea pigs. They are high in fat too. I feed mine rats, rabbits and quails.