I haven't asked Chris about it, but honestly the younglings are supposed to be "minutemen", lengthening their lifespan much would therefore defeat the original point. Up from 4 minutes to 5? Sure, at least as far as I'm concerned, but probably nothing higher.
A better next-attempt, imo, is to bring the tigers and vultures down to the same cost as commandos and weasels, then halve the build costs of all 4 of those, and double their base damage output (for the weasel might replace the damage buff with a significant health buff, since it's a kind of "butterfly tank"). Nanoswarms seem fine to me, though I'm listening about them too (they were pretty OP at first, then were nerfed).