A lot of good info here, but I have some also to offer.
The key problem is "lightly used" - that means the NiCd cells will develop a
memory, unlike more modern ones. A memory of being charged, then
leak-discharged, then trickle charged, etc, etc. The only good way around
avoiding this, is using (as others have said) a discharge cycle (or use to
flat) before recharging, and not leaving them flat.
The age of the cells has NOTHING to do with the expected performance, as
long as you have cycled them properly. I have NiCd cells still working
strongly from the mid nineties.