"I can be keen to do something, and i can be too keen. If I am too keen to do something, am i overly keen to do something, or so keen that i am not able to do something?"
Is it hopelessly ambiguous or could a comma help?
Yes, you can be keen to do something.
Yes, you can be too keen, too.
If you are too keen to do something,
It means that you want to do that thing
Very much so, overly so, so you say 'too keen'.
It doesn't say that you know how to do it
But you surely want to do it--so eagerly so.
"I am too keen to do something", and
"I, too, am keen to do that thing"
Are two different things, and
Commas will help to clarify the difference.
A word of warning: being keen on something
Does not make you unable to do that thing,
Or at least people wouldn't think so.
Saying "I am so keen that I am not able to do something"
Gives me a ring of a weird scene,
Such as someone was too keen to sing, but choked!