I am 13. Is it normal just to have pre-cum and not semen at this time? When will I be able to ejaculate?
While we think of ourselves as a single body, that body is actually composed of many systems that work together. You pre-ejaculate fluid is produced by the Cowper glands. You semen is mostly produced by your seminal vesicles. Since two different glands are involved, it is common for one to develop before the other. Eventually the whole system comes into play.
For about half of the boys, the seminal vesicles start producing in stage 2 of development. For the other half they don't start working until stage 4. The Cowper glands usually start in either stage 3 or stage 4. Therefore, when you can expect to start ejaculating will depend on what stage you are in in your development.