As others have said it's not about knowing stuff but about their social and emotional abilities. Is he comfortable about leaving you? Is he toilet trained -and independent (had a 3 yr old start who was supposedly fine but asked me to hold her on the toilet!)? Is he able to occupy himself? And follow simple instructions? Can he share? Does he have tantrums?
Even better if he can change his own coat and shoes too.
If your little boy was 3 in December then he is eligible for his 15 hours of funded sessions (if he is in England).
I agree with all the others, that at this age, academic knowledge is less important than social and emotional development.
I think that most children are ready to spend a little time away from their parents by the time they are 3. In the nursery where I work, children like your ds who will get 5 terms of funding often start off doing fewer than their 15 hours e.g. 3 x 3 hour sessions, and build up to their full 15 hours in the year before they start school.