I am 12. Is it normal to pre-ejaculate but can't have a real ejaculation during orgasm? I am very well developed for my age and I don't know what I am doing wrong.
It isn't what you are doing is wrong, it is that you are being impatient. Pre-ejaculate fluid comes from your Cowpar's glands. Semen comes from your seminal vesicles (mostly). They are two separate glands and they develop at different times. Some boys have pre-ejaculate first, others have semen first.
Typically the ability to ejaculate semen comes in either stage 2 or stage 4 of development. About half of all boys start in stage 2 and the rest start in stage 4. When it will happen for you will depend on your genes.