What is the bandwidth of human speech? What is the actual frecuency bandwidth of human speech. 
I know there is variation for gender, age and so, but what is the general range... I seem to find different ranges. 

Like here http://recognize-speech.com/preprocessing

Is the range defined between 100 hz 8khz 

Telephones are made to work in the ranges 300 Hz to 3400 Hz, according to Wiki: https://en.wikipedia.org/wiki/Voice_frequency

The hearing is in range
That really depends on your requirements and on your exact definition of bandwidth. 

Telephone range (300 Hz-3.4 kHz) has okay intelligibility but the quality of the voice is fairly compromised. For example it's hard to tell the difference between "s" and "f" sounds.  

80 Hz to 8 kHz gives you very good quality, although it's still possible for the human voice to make sounds outside of this range. Someone like James Earl Jones can easily go don to 50 Hz and specially trained singers can go a lot lower. Some fun examples at https://www.youtube.com/watch?v=lkdMl1ITw5M

If you want all of it, you should go for the range of hearing which is about 20 Hz to 20 kHz.