I started playing RM in the late 1980s. The first game I played had 20 players, mostly aged 12-15 and a handful of adults. The GM did something that I have always duplicated in games: Delegate authority. Since two of the players were US Army veterans, we were placed in charge of the two squads of players. The Dwarf Fighter was in charge of Alpha Team, made up of the front line fighters which made up a dozen of the players, and I was placed in command of Bravo Team, who were the support unit of Spell Users, the Healers, the Cleric and me, a High Man Rogue.
The setup was taken from WW2 German squad doctrine, where a squad leader could inflict more damage to the enemy by directing his squad, and observing the action, instead of taking direct participation in the fighting.
I've run campaigns and if there are more that five players, I divide the group into teams. The team/squad leaders are then responsible to keep their assigned groups in order so the gameplay is smooth and without disruption. When the respective leaders are familiar enough with the game, I even allow them to handle the combat resolution involving their team as subordinate GMs, which is also a good way to train future GMs.
Now that I am retired, and living thousands of miles away from my regular gaming group and mobility impaired, I still manage to get my Rolemaster fix with friends in Honolulu and San Francisco, through Discord. We tried Skype for a while but it didn't work as well for the Mac users.
People who really want to game will find a way to game. I live near a military base and I'm sure I could find players if I advertised but I live 20 miles from the nearest game store so my GM, who recently suffered a stroke, agreed to contact the people willing to set aside one night of the week and hold regular Rolemaster sessions over Discord. Discord has a die roller that all players could see, so it works for us.