When does old age begin?
Just to get things started a selection of views from friends locally:-
When your forgetory becomes better than your memory.
When the earth doesn’t move but the floor drops further down.
That gentle slope up toward the town gets jacked up into a steep hill
And a more serious one when dexterity is replaced by clumsiness.
When your future is all in the past.
Note I do realise some will find it difficult to remember that far back.