I'm old, and she engineered break up! (8)
I believe the answer is:
demolish
'break up' is the definition.
(thesaurus)
'i'm old and she engineered' is the wordplay.
I cannot really understand how this works, but
'i'm' could be 'i' (I've seen this in other clues) and 'i' is found in the answer.
'old' could be 'o' (common abbreviation eg in OE for Old English) and 'o' is found in the answer.
'she' could be 'em' and 'em' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for demolish that I've seen before include "Break down" , "Knock down, a building or argument perhaps" , "Bulldoze" , "Knock down, say a building" , "Destroy completely" .)