There are already age restrictions on some government positions (by which I mean, upper age ranges; I dont mean the lower age limits say for president that already exist). I'm sure that could be extended to government positions. I imagine - and I'm not a legal scholar - that the problem would be discriminating against an individual based on age but if there were blanket upper age limits that would probably be doable. Of course, the old heads making the laws aren't gonna legislate themselves out of a job.