While varied in some countries, AppleCare+ can generally only be purchased within 60-days of the original device purchase.
Buy an AppleCare plan - Apple Support
You should note that AppleCare+ is an insurance product that can only be purchased prior to occurrence of damage. If your iPad has already suffered damage, you cannot add this cover.
If you have waited too long to add the optional AppleCare+ plan, or you are not eligible, you can still access Apple’s authorised repair services. You can check costs here:
iPad Repair & Service - Apple Support
Repair can also be arranged through the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP):
Genius Bar Reservation and Apple Support Options - Apple