Hey Ipeacok,
Don't worry about your age.... Yes you have to be 21yrs old to be allowed to work on a full licence as a validated conrtoller on your own....
However, by the time you will be fully validated you will have reached the age of 21... Before that time you will be working under a Student Licence which does not have any specific age limit on its own.
Regarding the fact that you can only choose dates within the next two week I don't see any problems.... All you have to do is go through the 25pages you recieved and maybe to relax yourself you could do a few example tests on the internet. Besides the motivational test (this does not need 2weeks of studying/ if so you will be having many problems with the theory to come since you can expect around 3500pages in about 3months) , the is no need for study, these test are designed to check your abilities, you way of thinking, things you either can do or you can't.
Anyway,
Just book your test within those 2weeks, go through the motivational papers, look up some test example so you kind of now how they look, have a good rest prior to your test and try to be as relaxed as possible when you go do them.
Good Luck....