Will I ever be able to change the year-of-birth on Facebook?
You can change it now by going to your profile, and under the About section click Edit. Not only are you limited by the number of times you can change it, but if you're changing it to be older/younger than 18 they're onto that trick. :-)
Yes but there is only a certain amount of times you can change it I think 3 but i could be wrong
Once you are 18