For starters - that's a nice fatty you have there.To find the actual age of the snake you will need to do the following:
1. Count the scales (on the top) from the bottom of the vent to the tip of the tail.
2. Count the number of teeth from the top jaw only.
3. Divide the teeth number into the scale number.
4. And you should come up with a great looking BP, because that's what I see.
You can go to a local Herp vet (if one is available) and find out what they would charge to identify the sex for you? At that point, ask a bunch of questions.