The first ejaculation is the first time semen comes out of the penis. From this moment on the guy is able to father a child.
Most guys have their first ejaculation between the ages of 11 to 16, normally a year after the penis has significantly increased in size. The average age at which it occurs is 13 years and 2 months.
About 20% has the first ejaculation at night, two thirds has it when they masturbate and 15% during sex.
The time of the first seminal discharge is set by hormones. A guy can do nothing to change this timing. But you can come to orgasm even if the sperm factory is not working yet.
If you are 16 and never ejaculated you should visit your doctor to check out whether you are just late in your physical development or if something is wrong.
To prevent unwanted pregnancy you have to use condoms when you have sex, also if you never ejaculated. The first ejaculation can come unexpectedly and with a condom you are also protected against STD’s.