I'm not sure you realize how strange this question is ... and also how irrelevant.
First of all, the learning process of anything depends on a person's capacity to learn and adapt their thinking. You can be 50 and master it in 2 days of reading and practicing, you can also do it in 2 hours or 5 years, it's up to your capacity.
For me, it took about two weeks, when I was 19.
Second of all, learning a programming language and learning how to program are two different things. You can know a language perfectly, but if you don't know basic algorithms, object oriented programming, design patterns and at least some bit of other web stuff like CSS and javascript, simply learning the language won't do much good in finding a job. Most web-dev companies put more stock on these things than the actual PHP language exactly because of what I said above: a language is learned easily, but programming is the hard part. The theory of these things can be learned in weeks, but being any good with them takes years (just think a computer science student studies OOP and design patters for a few years in university and very few are actually any good with them after graduation).
