Fast start, lot of help and great opportunities
I started learning PHP after I had mastered HTML and CSS, I started learning PHP back in 2001, so I've got a few years left to develop in PHP.
PHP is a wonderfully easy language to go to and learn, there is really much help to get from orther on the internet and there are many who are diligent to help you if you get any problems or have any questions you would like some help.
There are a lot of open soruces projects that use PHP eg. Wordpress, Dupral, osCommerce, Magento, PrestaShop Mantis Bug and many more projects are made in PHP, so you can give PHP a number of options that develop to get started with your projects.