I'd say this idea itself is already quite controversial and far from settled. Old people are not necessarily worse off in their abilities to think or their "creativity" or whatnot. Children might come up with a load of ideas because their knowledge has not been trained/structured in the same way as the adults have yet. But that doesn't mean their ideas would be particularly useful in solving real problems, since they tend to be far less reality-based.

Also there are psycholinguistic researches at my university that suggest old people don't actually learn more slowly, they have just pruned some nonsensical connections and consolidated knowledge based on real world experience, and are thus worse at learning invented examples that might not make much sense.