I purchased a 3rd floor condo in 1998, that is adjacent to a 2 floor condo. My condo when I purchased it came with a deck that was installed in 1989. In sits on top of the 2 storie condo, I have exclusive use to the deck and it is enclosed.It has a wrap around railing that sits 4 ft high and vertical boards that keeps it enclosed. It sits 15 feet from the nearest ledge on either side.The only opening is a door attached to my condo. The board prior to the time of my purchase had grandfather in the deck. Thus preventing other tenants for also building a deck, but allowing the previous owner to keep the deck.
My new and current condo association board members want me to take it down. They say that it's a safety concern because it's on the roof. In all the years I've lived here,I have never set foot on the roof. Only on my deck.Not to mention what an effort that would be to climb over the deck to get on the roof.

Can the Condo association make me remove this deck after it's been up for so many years? Even though it's an exclusive use deck?

Only if they can prove that there is some structural issue that has arisen because of age that could damage the roof its built on.

Hire an engineer to tet the deck and present the findings to the board. If the deck was grandfathered in and its part of the registered structure with the county. They will have a hard time forcing its removal.