Why do we have different voices?
A person’s voice depends on a lot of different factors, such as the exact shape and size of the voicebox, the shape and size of the mouth and the way in which the person has learnt to speak.
Even if we considered two identical twins, the way they were brought up could affect how they speak. Our vocal system is quite versatile and adaptable and so can produce a variety of different sounds, and different people may prefer to speak in particular ways for all sorts of reasons.
(Also men’s voices are deeper is quite simple; testosterone production during puberty causes the voicebox (Adam’s apple) in males to increase in size. This causes the vibrations of the vocal chords to have a longer wavelength, which in turn reduces the frequency (pitch) of the sound we hear)