I really wish you would stop posting incorrect information everywhere.
You don't need lower tier medals to upgrade your GH. Higher tier medals can be used in their place. One gold medal is equal to two silver medals, and one silver medal is equal to two bronze medals (by extension, one gold is equal to four bronze medals)
As for if anyone has maxed it, I wouldn't be surprised if the answer was yes. The game has been out long enough that those who joined at the start and have continued playing regularly, likely have accumulated enough medals by now.