Crossword Genius

Rampant ill health's so sad at this great age (2,3,2,3,5)

Ross

I believe the answer is:

as old as the hills

I'm a little stuck... Click here to teach me more about this clue!

'this great age' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'rampant ill health's so sad' is the wordplay.
'rampant' is an anagram indicator (I've seen this in other clues).
'ill'+'healths'+'so'+'sad'='illhealthssosad'
'illhealthssosad' with letters rearranged gives 'AS OLD AS THE HILLS'.

'at' is the link.

Can you help me to learn more?

I've seen this clue in The Guardian.
Want a hint initially instead of a full solution? Install my app