Hi Dan, I prefer combs to consist predominantly of worker comb (at least 90% worker) in preference to age of comb. My first mentor gave me a rule of thumb guide to determine when comb is too old. It’s when you can’t see light through the comb when you hold it up into a light. Otherwise a comb can be used for honey indefinitely.
However when choosing a frame of brood to use for a colony to make emergency queens from, that frame doesn’t have to meet any of the above criteria. It only needs to have some worker eggs of very young worker larvae. Preferably from a good producing quiet colony.