For me, the first signs of old age were filling a rucksack with polystyrene to make a portable seat. What really brought it home however was having to sit while taking a shower. Now, I literally cannot get on and off a bus without my walking stick.
I have spent my entire adult life jumping in and out of lorries, trains, aeroplanes, boats and even, on a couple of occasions, helicopters. A few weeks ago, during rush hour, a bus driver shouted at the other passengers to clear a seat for the 'old guy'. Rather than being humiliated, I was actually very grateful. My gratitude, in my view, is definitely a sure sign of advancing age.