I think time wise that would be the limit, but I think you will still get a tasty succulent bird on your table if you cook it slowley. In France the markets start to sell goslings in June and they are slaughtered for Christmas - so at six months old.
We don't restrict ours, but if you are worried about developing too much muscle because of the age, then put say two in an enclosure and let the others do their thing. As long as they can move around comfortably and are happy it will be fine. Give them a bath to duck and dive around.
Ours get fed ble and vegitation and have always tasted fantastic. Other may have other suggestions.
Hanging is a personal choice and there is another thread about this on here talking about turkeys.
Hope this helps.
Kate