The pair of sentences in the OP are not good. I wonder if this is an "acceptable" translation - because it's certainly not the "best translation." There's not a big difference between most old and least young, but there is a difference, and it should have been preserved in the translation.
My word bank gave oldest as opposed to least young as the answer. The answer above "You are the least young of us" does convey a thought. But I myself being a native English speaker find it odd, wierd and awkward. Also instead of oldest why not eldest? That really seems most appropriate.