Hi, i'm 16 years old, my height is 191 cm, my voice broke a year ago(broken because of puberty), my penis is 12 cm long. personally, this does not suit me and i would like to increase it. how can i increase it and in general is that normal length?

You are normal: Some people are tall like you & others are much shorter & still within normal range. Penises also come in wide range of normal sizes from smaller normal, like yours to larger normal like others.50 - 70% of men yearn to have larger penis. Penises seen in porno movies are the exception & many don't work that well in real life.Medications, equipment & surgeries to elongate penises are all fake news.