As an older programmer (say, 50+), learning new programming paradigms is easy. Hell, absorbing new frameworks, programming languages etc. in a week or two is still a piece of cake. Why? Because that's not too far from the domain you know. BUT, diving into totally new application domains requires a lot more efforts than when you were younger. As an example: if you've never been exposed to an EE education and you suddenly have a project about, say, writing an antennae simulator, you'll have to absorb Maxwell's Equations, and related maths. Even if you've had CS training with maths background in your prime, you'll definitively need a lot more time to wrap your head around this with 50, 60 than if you were in your 30ies. That's not impossible, of course, but the additional time to understand this new domain, and apply it to programming, will slow you down so much that companies will often refrain from hiring you, despite your immense wealth of additional side-knowledge that could be very useful.