My 9 and 10 year old terriers are not showing any signs of slowing down, at all. The 10 yr old runs circles around EVERYBODY, literally. He follows when we're riding the horses and keeps up with them when all the other dogs have given up and are laying in the shade...so no 5 isn't even remotely old for a terrier!I need to find a club or something. I don't think the age of 5 or so is too old? ... they say Terriers are long lived and a fairly healthy breed ... my childhood terrier lived to be 17 years old.