Hate to say it, but it's the age group that's hurting you guys. The older guys just don't want to be out there playing all the time, especially moreso if they're already playing regular league during the week. Where I live, I see the old guys practice one day and play another day during the week. They're not out there all the time like the younger guys are.
You need to find out what incentive they'd like to have to play in this ladder moreso than the actual satisfaction of playing. Free gear from the club for the top rung players, club recognition/VIP treatment, maybe a discount on court fees for the next league season, etc. The old guys want to play for something other than self-satisfaction because their bodies hurt.