Is it normal to have underarm hair at 11 years of age? I have no other signs of puberty yet.
Yes, it is perfectly normal, especially for girls. The order of development is more variable for women than for men for some reason. I do suspect that other signs are probably there, but because they come so gradually or smoothly they are overlooked. You can use the Tanner Stage Calculator for Girls
to determine your progress. If nothing else, the questions will make you aware of the many signs of puberty.