I think this 'increasing retirement age allows more commands during an expansion' theory is a little like the trip fuel adjustment. Some people get it and some people don't! It does sound convincing to say that by keeping on C+Ts we can facilitate more expansion....bollox!
If every C+T is 54 then CX has the ability to 'extend' them until 60...but it will cost them in bypass pay. So how is RA55 a constraint? If they don't extend them they will have a higher rate of command courses as they will need to upgrade people to C+T from line captains and then replace those line captains with new captains! So even extending them is bad for commands but at least you will get bypass pay!
Whether it is 30 or 300, it still has an effect. How many commands last year???? 60+? So even 30 will delay command for up to 6 months.