Yup, I remember doing a breakdown once, I am sure it was like 10-15 years ago. And things have changed since, but at one point it was ridiculous. Roughly like 12 of the 15 top Ds in the league had taken huuuuge steps after they were 26-27 y/o. And many had even gone from being marginal NHLers at like 25 to being top guys post 27-28 y/o. If I remember correctly guys like McCabe and Souray (top of the table in D scoring), guys like Dan Boyle and Rafalski that were talented but that didn't breakout before late 20s, a euro like Vishnovsky, Chara and so forth populated that summery.
Someone mentioned it in a reply to me recently, that this isn't really the case anymore, and that sounds plausible from just observations that I've made. More and more young Ds are getting big roles early. But at the same time, its a long road. Being able to just hit the ice and score a ton and be hot for a couple of seasons is something else than becoming that top guy that really changes the outlook of the play when he hit the ice. Q Hughes, Makar and co. aren't there yet.
My point is just, for Miller the time frame shouldn't be for him to get warm in his cloaths by this time next season. Its 4-5 years down the road.