I think fit may be the key difference between "old-man" chinos and the more fashion-forward variety. If they're high-rise, loose in the seat and thigh but tapering down to the ankle, that will definitely project an older, stodgier image. But chinos that are either slim and straight, slim and tapered, or loose all the way down can definitely look youthful. I've yet to see a true bootcut chino (not including jean-cut cotton pants).
In regard to the 5EP's, based on the company's philosophy, I imagine these pants are an attempt to recreate the original military variety, hence the higher rise. With that 12 inches of rise, though, the 32" inseam may be enough for taller guys too.
I don't know much about Bill's khakis, but I believe they are also intended as a militaryesque quasi-reproduction. They're also half the price of 5EP. But just based on their marketing and target demographic, I wouldn't dare recommend them to someone seeking a "youthful" pair of chinos.
I think your best bet would be Yoox...they always have a wide variety of this sort of thing, both from more well-established makers like Weber and Mason's and also a ton of labels you've probably never seen.