When you say 'not so keen, ' are you dead set against it, or that it might not be bringing in a lot of money, so you think you'll be working for peanuts?
Can I make a suggestion?
Give your dad a month to train you (No messing about on your behalf, or laziness. Give it 100%)
THEN if at the end of that month, you can say to your dad you tried your heart out, but it just wasn't to be.
If you don't, it COULD be something you'll regret long after your dad is no longer around.