Was the questioner mature when he committed acts of masturbation, consumed alcohol, and broke his fast in Ramadan at the age of thirteen, given that he experienced his first wet dream at the age of sixteen, and is he accountable for these actions at that age?

If you committed these acts before puberty, there is no sin upon you and nothing is required of you, because the pen is lifted from the child until he reaches puberty. However, if you did any of that after puberty and repented to Allah Almighty, then "the one who repents from sin is like one who has no sin." As for masturbation during the day in Ramadan, if it does not result in the emission of semen, then your fast is not broken by it. But if semen is emitted and you have reached puberty, then your fast is invalidated if you were aware of the ruling. If you were ignorant of the prohibition of masturbation and its invalidating effect on the fast, then your fast is not invalidated by that.