I think the milestone is when you make a noise of any sort when you bend over.
Either from your sphincter or a gentle 'aaaaoooooffffff' from the mouth.
Very dangerous. Soon you'll be looking at those trollies on wheels and remarking what a good idea they would be. Buying shoes for comfort value rather than style. Leafing through those magazines you get with the Sunday papaer and thinking 'how have i managed without that'. Spend an inordinate amount of time 'pottering about'. Actually know how to potter about. Going down the pub by yourself for one pint and to read the paper.
It's a slippery slope from here mate. Get off while you still can.