Nah you aint too fat. You should go Boxing right now, you will lose some lbs and you will get more strenght!
Don't lose too much lbs tho or else you will lose your power, you will be faster but with less power, try to maintain your lbs how you like it!
You may be too fat to compete right now, but mostly because you're probably not in shape. You will likely lose some weight, but you'll get healthier which is more important. But the bottom line is, if you want to take up boxing, just go do it. Don't let doubt get in your way if boxing is what you want to do.
Never underestimate a fat guy. Buster Mathis was 300 lbs, but was very good at boxing and several have started and lost weight as they trained and fought. Go for it .Most heavies today are in the 240 range, but yes, are 2-3 "taller, but still don't quit.
No you can't be 'too fat or unfit' to train. That's a lazy statement.
Im 19 6ft 270lbs and would like to start boxing but im afraid im to fat to train and compete.