I don't think a few months in age makes that much of an impact for a kid that just turned 18 two months ago. I'd weight overall experience far more and they all had basically the same amount when entering pro ball. Having an entire professional offseason to develop, train, and mature prior to going to single A is a significant preparation advantage over a few months of age difference.
I guess a better way to express it, rather than age, would be signing date. The deadline used to be later. Owings, Lindor, and Harper didn't even sign until August 11/15/16, respectively. Lewis isn't really doing something they failed to do in their first year, so much as they didn't have the chance.
And actually, Mike Trout did get promoted to the Midwest League in his draft year, on September 1st. And he signed about 2 weeks later than Lewis, so it's roughly an equal accomplishment, I'd say.
Of course, pointing out the other circumstances around his promotion is hardly being critical of Lewis. Still an outstanding group of comparables!