It is VERY important to register early if you plan on going to nationals!!!
Last year I registered for 35-39 about 3 weeks late and got a start in the low 100's... then I registered for the B's about 6 weeks late and was THE LAST RIDER out of about 150!! Don't wait.
FYI, you will need to have a valid USA Cycling license... so chances are that means you will need to renew it!