After thinking about it, I am not sure a state can regulate a much older buck age structure. Most state dnr’s are answering to too many entities to manage deer for a singular purpose. States are trying to hold deer populations in check to pacify insurance companies, farmers, suburbanites, disease management, etc.
For example, in Iowa, an estimated 167,000 hunters harvested approx 50,000 bucks. I am sure a number of them didnt hunt at all. Some probably didnt hunt very much. Are that many folks hunting and not seeing a buck - or are most passing a buck(s). In my experience, typically the smaller the acreage controlled, the less selective the hunter. Probably like many states, the better quality deer areas are usually those where hunters are more protective of their deer - and probably have higher deer densities than normal areas.
I think for states alone to be responsible for maintaining a mature age structure - they would have to have regulations in place that would be very restrictive on buck harvest - and that would eventually skew the buck doe ratio, and probably increase the deer density. States out west may be more successful because hunters out there have previously practiced limited license quotas. It would be a hard sell in the eastern half of the country - and especially the south - to have to participate in a drawing to deer hunt - especially on land you own or lease.
I think states can provide a starting point towards quality deer management - but the hunters have to be willing to carry it all the way. I know ten guys who leased 800 acres near me last year and they killed one buck but passed a dozen. I had nine hunters on my place last year, and we killed two bucks. All of them passed bucks. I think it would be very difficult for states in our area to assume a management program supporting a mature buck age class. As said above, it would probably not be very popular.