I agree with Tony, but I wouldn't go for one as long as 10'. A long longboard is a mission to manoeuvre in the water for anyone, let alone a beginner. I would go with a shorter one in the low 9' range, 9'2" is a common size. Try to get one with lots of width (23-23.5 inches).
I would agree a 10' board is harder to maneuver, but we have found in giving surfing lessons to countless people using 9', and 10' surfboards, the beginner on the 10' longboards do much better and have a lot more fun with the 10' longboards, and they learn to surf much quicker. With that said if we were talking about a kid that is much lighter the 9' longboard might be fine, but with someone in the 220 lb range you will do much better on the 10' longboard. You will get better much faster and then you can learn to maneuver. That is what I have found from giving surf lessons. I think the width suggested sounds good!