I think PHP (5.x/6x) is still applicable to any developer, new or old, experienced or not. Many of us cut our teeth on PHP's simple scripting concepts, and that shouldn't change. And from what I've seen from past history, it won't.

There is a tremendous amount of backwards compatibility in current versions of PHP that allows one to follow the same approach to Web development that those did back 10-15 years ago with PHP 4. No, it is not "Enterprise", and yes there are security considerations to account for. But the process of adoption is key, and PHP continues to be adopted by a lot of startups/projects. Those that choose to adopt the PHP language as their advanced vernacular moving forward still continue to have a number of more advanced programming language concepts to utilize in PHP with each new release, with barely any breakage with other approaches to using PHP.