[whiterknight]

The longer I am around the less true I find this. Can any good developer learn and contribute with a new language? Yes.

But there is also a peak performance achieved by using tools for decades that is not transferable. C experts didn’t switch to Java, they found different jobs.

For your core technology you want a few of those 5-10+ year guys.

[bluGill]

Sure, but you only need a few of those 5-10+ year "guys". The rest can be behind and will develop those skills over time.