Yes! Getting interested in compilers was my hook into professional CS (previously I'd been on a route to EE, and only formally switched sides in college), it's a great way to learn a TON about a wide range of computer science topics. You're a bit younger (I was in high school when I started fooling around with parsers and interpreters), but there's a whole lot more information at your fingertips these days.
Start small: Design the tiniest language you can possibly think of -- start with nothing more than a simple math calculator that allows variable assignment and substitution. When you get adventurous, try adding "if" or loops. Forget arcane tools like lex and yacc, try writing a simple recursive descent parser by hand, maybe convert to simple bytecodes and write an interpreter for it (avoid all the hard parts of understanding assembly for a particular machine, register allocation, etc.). You'll learn a tremendous amount just with this project.
Like others, I recommend the Dragon book (1986 edition, I don't like the new one, frankly).
I'll add that for your other projects, I recommending using C or C++, ditch PHP, not because I'm a language bigot, but just because I think that working through the difficulties in C/C++ will teach you a lot more about underlying machine architecture and compiler issues.
(Note: if you were a professional, the advice would be NOT to create a new language. That's almost never the right solution. But as a project for learning and exploration, it's fantastic.)