"She was huge of frame, terrifying of aspect, and with a harsh voice. A great mass of bright red hair fell to her knees: she wore a twisted torc, and a tunic of many colours, over which was a thick mantle, fastened by a brooch. Now she grasped a spear, to strike fear into all who watched her." Dio Cassius
I also thought that she was at least in her 30s or 40s, which would make her late-middle-aged for that time. Watch them get a skinny little 25 year old babe to play her.