From Longman Dictionary of Contemporary Englishbe keen on somebody/somethingbe keen on somebody/somethingBritish English spoken to like someone or something I’m not keen on cabbage.not too/not very/not that keen on something She likes Biology, but she’s not too keen on Physics. My flatmates want to have a party, but I’m not keen on the idea. → keen
Examples from the Corpus
keen on the idea• Her father, terrified of what the photos show she has become, was not too keen on the idea.• She wasn't keen on the idea at all.• She is keen on the idea of an international convention on the atmosphere.• However, health authorities and family practitioner authorities are keen on the idea of generic teams delivering patch-based care.• She seemed to consider the proposal favourably and Princess Margaret, who I knew was keen on the idea, was supportive. 