He turns 24 in January, so he'll no longer be a Young DP.
Why is Kaku's cap hit going to double?
Edit: Actually, I guess that he won't, based on this language. He'll still be 23 for a portion of the "league year".
"Young Designated Player
A Designated Player who is 23 years old (or younger than the age of 23) during the League Year (the age of the player is determined by year - not date - of birth) will carry the following Young Designated Player Salary Budget Charge:
Ages 20 and younger: $150,000
Ages 21-23: $200,000"