I think there would be a limit in terms of how old a marine would be when they are sent to the DW as the marine gets older they are likely to get killed easier i believe as even space marines feel their age at some point.
If you plan on being old then its likely you would be on permanent secondment to the Watch.
I think its really up to interpretation.
Marines never really get to live long enough to figure out what their "natural" lifespan would be.
Edit: Also my Character being a Permanent Member might make sense though as well. As the Chapter I chose has no Lore, but is an Official GW Chapter.
Last edited by LordNecross; 04-08-15 at 07:30 AM.