My son started around age 7 and he is 11 now and loves to play. 6 is on the young size due to finger strength and attention span, but worth trying (as always, depends on the kid.) The teacher will tell you if they think it will work or to wait for a few years.
We had good experiences in the Seattle drum school in Georgetown, and with Richie Jenkin who teaches from his home on Alki. Good luck, and remember if it doesn’t work out now, sometimes waiting a year or so and revisiting the whole idea is a good way to go.