Age is irrelevant in software enigneering, I could have done the same thing at 13.Oh...I thought you were older, with a cart load of experience behind you....but that was great, indeed...
No computer generated number is absolutely random unless you can introduce real random entropy.
Using a low-level PHP function might be able to use a server's MAC address but in PHP is you really wanted random, you could pull the data from various active/busy web sites and calculate a hash based on that data.
The idea being, that people who submit messages to a website are more random then a super speedy ticking clock.