BMI is a load of b*ll*x! It's far to simplistic to be of any real value.
I remember reading that, for some reason, the BMI thresholds were reviewed in the US, and at a stroke several million Americans were 'overweight' rather than 'normal'. Which just shows how daft it is - one day you're healthy, the next you're not.
Don't worry about it. You sound very healthy to me - I'm envious!
BTW, I believe Brad Pitt is overweight by BMI standards, and George Cluney obese. And as tonyted says hundreds of top sportsmen are obese & worse.