Contrary to popular belief, it is not just the RAF who can (and have) extended to 60; the Army certainly can but I don't know about the Navy. The Navy rules always did confuse me and I am pretty sure they had to go at 50?
There was also a 'grace period' for the older employees which meant they didn't have to transfer onto any new scheme (pay 16 etc...). If he chose to change ToS, there would be different rules and the 2 year is probably one of those.