I've been with my partner for just over 12years, last year he was told he has hiv, he takes no meds, his cd count is 500+ how long has he had hiv?

It's variable: Here are some statistics: 25% of people infected with HIV will progress to a CD4 count of 200 in 1-2 years; 50% will take 2-10 years; 25% will take 10 to 15 years! Normal CD4 is 500 to 1200 cells/mm3 and general guidelines says to start antiretroviral therapy, for sure, when CD4 is 350 or less. Some recommend starting sooner. Have your partner review again with his doctor. PRACTICE SAFE SEX:)

It could be years: There's no way to know duration of your partner's HIV infection from this information. With near normal CD4 count, it's likely he has had it less than 5 years, but some people maintain their CD4 levels for 10+ years. It is a concern and surprise if he hasn't told you about his HIV for over a year. You may be at very high risk yourself. Get tested ASAP and start using condoms with him.