I'm wondering haw old do you be when you get sperm
There is no set age when you produce sperm.
It depends on what stage of puberty you are in and when your body reaches the point where you start producing sperm for some guys it can be around 11 and for some as late as 15 or 16.
It will happen when you reach that point in your development.
Many young guys who are just starting puberty find that when they masturbate, from which they derive intense pleasure, they have an orgasm but nothing comes out of their penis (no ejaculation). This is called a dry orgasm.
Boys start puberty at different ages so the age of first semen production varies. One has to be in puberty a year or longer before semen production starts, so there is nothing to ejaculate. Although the muscle contractions to produce an ejaculation occur, there is no semen to ejaculate because semen production has not yet started.
When semen production does start, there will be only a few drops at first. It usually is clear instead of milky-colored. The quantity increases later and the color changes to milky white.
Just enjoy your dry orgasms while you wait. You will see some semen come out eventually.