The requirements for ranks after single All Star will get tougher and increase every 4 ranks (for example, the amount of required YYB games will go up to around 8-10 every 4 ranks) after you get Rank 20.
I know most Altador Cup-savvy Neopians already know it, but here's AbsoluteCorruption's Petpage that I forgot to link to where you can keep track of the requirements to your next rank plus a leaderboard with the overall top 10 AC players and top 5 AC players for every individual team. It has target ranks from the usual first 20 ranks and All Stars from single to quadruple, it sadly doesn't have individual target ranks after 20 to choose from.