Spoonley, Draper and Costa are all still in the under 20 category for next year, as your age is only taken into account in regards to how old you are when you sign the contract.
So you could get them on a 10 year deal and have them as under 20s forever?
As clever as that sounds - it is a 2 year maximum (i.e. 1 year whilst 20). Costa was the only one of the 3 that was eligible for a 3 year deal. Read the FFA website - spells it out pretty clearly