“I’m Keen” Means “I’d Like to Do It”

In everyday Australian conversation, when someone suggests a walk, a meal or a project, “I’m keen” means “I’m interested and willing to join”. For example: “We’re going for a walk on Sunday.” “I’m keen. What time?”

The strength can be adjusted. “I’m really keen” is more enthusiastic; “I’d be keen” is softer and often means you would join if the details suit; “I’m not too keen” means you are not very interested. The expression is natural in British, Australian and New Zealand English. Americans understand it, though “I’m interested” or “I’m up for it” may be more usual.

https://www.collinsdictionary.com/dictionary/english/keen
https://dictionary.cambridge.org/dictionary/english/keen