Put on openers -- absurdly easy, pinching runs for ages (7,5)
I believe the answer is:
Here is my best explanation:
'ages' is the definition.
(I've seen this before)
'put on openers absurdly easy pinching runs' is the subsidiary indication.
'put on' becomes 'don' ('don' can be a synonym of 'put on'**).
'openers' becomes 'keys' (I've seen this before).
'absurdly' indicates anagramming the letters (I've seen this in other clues).
'pinching' means one lot of letters goes inside another (taking inside).
'runs' becomes 'r' (cricket abbreviation).
'easy' is an anagram of 'yeas'.
'yeas' placed around 'r' is 'years'.
'for' is the link.
(Other definitions for donkeys years that I've seen before include "A long time (spent on Blackpool beach?)", "forever", "An age", "Very long time", "What's evident in old ass", "Beastly long time", "Yonks", "A beastly long time" and "Ages and ages".)