I usually hear "for ages", in BrE; but "in ages" is also used.
We can use "in ages" in other contexts, when "ages" is a countable noun, meaning "eras":
1. "In ages past, when the earth consisted mostly of islands of volcanic ash amid seas of sulphur, giant Adverbs roamed vast forests of monocarpic Conjunct...."
2. "Oh God, our help in ages past/Our hope for years to come;/Our shelter from the stormy blast,/And our eternal home." (First verse of a hymn once much favoured by British schoolteachers.)
See you later!
PS: I'm sorry I haven't checked those exercises for you yet...will do so soon...
- For Teachers