Learn D7 coding or D8?

I'm not a Drupal developer but a pro Drupal site builder. I can read PHP and able to tweak and even write some code. I was thinking about learning the development but came across this idea that in D8 we have symphony and some other big changes. Now the question is that shall I start learning D8 dev or I should start with D7 dev? - See more at: http://demo.weebpal.com/forum-plus/en/node/1#sthash.p70HJJcO.dpuf