Possible Clues:

• At the age of what one ate a mixture of
• Up with the aged cuppa! (3)
• Tea can make one aged shortly
• Up with something to eat for the aged, in short
• Aged, in short
• Shortly, the old tea will come up
• As old as can be made of the end of 20 across
• Comes up for a cuppa, as of old in short
• Shortaged, perhaps, to make the tea
• Shortaged?