Why not reservist till 60?
Simply, cuz S'pore doesn't need that many PDF units (which is what the oldie troops are good for by then).
Also cuz combat is always an adventure for the young. Yes, this applies more to conscripts all over the world -- who, if you read various war memoirs, already treat mid-twentysomething SGTs & CPTs like they're old-timers! Don't you NSFs also feel the same way? ~lol~
That said, the present 10-year cycle isn't decided out of the blue -- but instead streamlined based on how the countless batches had performed over the decades in their proficiency & fitness tests. I know, cuz I went through it (1989-2001). The reality was my outfit peaked at around our 6th ICT/10th year or so, when everyone was in their late-20s. Can't directly confirm this, but I think this period is when most qualified for the Best Reservist Unit competition too.
Thereafter, there was significant diminishing returns, with the overall commitment wavering due to outside factors (marriages, new families, promotion to middle management, starting own business, etc.). Conveniently or pragmatically, the units would be reposted to PDF command -- i.e. second-line troops -- during this time, while certain commanders chosen to recycle on sent for upgrading courses. Winding down, the rest of the troops could look forward to be deactivated (MINDEF reserve) by their midthirties.
I don't envision any drastic change to this system, as long as we're in peacetime.
