As far as I know you have to buy Apple Care WITH the computer. You might be able to get it now, although I've never heard of anyone doing it. Good luck!😀
You can buy the Apple Protection Plan anytime but it must be registered using the computer's serial number NO LATER THAN 1 year after the original purchase date of the computer....
So if you purchased in January 2009 then you have missed the boat unfortunately.....
APP only covers for 3 years (including the first 12 months) so even if you had purchased it in January 2010 it would only have covered you for the next 2 years....not the next 3 years.