I am 40 years old was blessed with good genes and have always had big arms have gotten as big as 20 7/8 left arm 20 1/2 right arm but have never been able to get bigger than that . I can say that I personally have never gained more than 1/2 in in a cycle once I hit like 18 in my opinion it takes much longer to keep getting bigger as your body hits you genetic plateau. As for those who say anything over 18 od rare I suggest you go to one of the bigger shows like thre Arnold Classic and see some of the monsters not even competing lol it can be quite humbling.I also think the length of your arms also makes it easier to gain mass, as I am 6 ft but my reach is only 67 inches , so it is easier I think than for a man with longer arms