+/1 18 months from its real life certification date
From the manual
Each aircraft model has information about production start and end dates in the master database, these are the real dates of the real aircraft model. For simulation purposes these dates are randomized for each game world with a maximum variation of +/- 1,5 years for each model. This game feature makes the simulation more unpredictable as players cannot know when "their favorite" aircraft model is launched and then wait for that date to come.