Precaliber 20 or 24?

My son is almost 7 years old and is 50” tall. We went to a Trek store today and the sales guy said since he’s right in the middle of the 20” bike range, we should size up to the 24”.

My son is currently on a 16” Schwinn and recently learned how to ride it without training wheels. He definitely needs to size up but the 24” looked so big.

He was able to swing his leg over when he tried it in store.

Just trying to know if we really should skip the 20” and go right to the 24” even though he’s below the height range.

Thanks!