Guide to how old one is, cheapness of passage is (8)

I believe the answer is:

steerage

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'cheapness of passage is' is the definition.
I can't judge whether this defines the answer.

'guide to how old one is' is the wordplay.
'guide' becomes 'steer' (synonyms).
'to how old one is' becomes 'age'.
'steer'+'age'='STEERAGE'

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(Other definitions for steerage that I've seen before include "Cheap seats" , "Part of ship with lowest fares" , "space on vessel" , "It's the cheapest way to go by sea" , "Cheap accommodation on a passenger ship" .)

I've seen this clue in the Evening Standard.

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