One of the best engineers I have worked with is on his 60's. When I worked with him, the rest of the engineering team had an average age of 23 or so (me being 32), but this guy could give everyone a run for their money. This is not about age, but about staying current and sharp. Keep learning, and you won't have this issue. Sure, a guy fresh out of school has a ton of energy and works crazy hours, but as an Engineering Manager and Product Manager I knew that if I needed something to be really done on time I could always trust the older (and quite frankly way smarter) guy.