This is an English expression that is used widely throughout the world when UK versions of English are used. However, it is very rare to hear it in American English. Nearly all Americans are familiar with the expression though so if you use it they will understand you. The times when it IS used in American English, it is usually used in the negative (example: "She is not very keen on pizza"). The strength of the expression would depend on the speaker, their tone of voice, and the context. It can be a little, or it can be a lot. Most of the time, I would say it falls somewhere in the middle.

In short, this expression is used in cases of travel to the UK and other commonwealth territories or time travel to the 1950's America :)

Keen means to be very enthusiastic or excited about something or someone. You can say 'She wasn't keen on going to the party.' meaning she wasn't very excited about it. The only time I ever heard it used was in movies from the 50's in the US. It was a popular word among teenagers at the time.

Yeah, keen is used in many ways. Although, the one I hear most is when someone is attracted to someone else. "I've been keen on her since she shoved me into the pool". :)

Hi! to be keen on means : to be mad about , to be fond of or to like . bye