1. Broadening of chest and shoulders

Onset of puberty brings many physical changes in boys. Their chest and shoulders broaden and their muscles start to develop.

illustration of broadening of chest, shoulders and development of muscles during puberty in boys from age 9 to age 19 - Menstrupedia
2. Deepening of voice and appearance of facial hair

The voice gets deeper. Hair begins to grow on the face that later develop into moustache and beard.

illustration of appearance of facial hair during puberty in boys from age 9 to age 19 - Menstrupedia
3. Appearance of body hair and pubic hair

Hair begins to grow on the chest, in the armpits, hands, legs and in the groin area. Hair in the groin region is called pubic hair.

illustration of hair on the chest, hands, legs, armpits and in the genital regions of a man - Menstrupedia
4. Increase in size of genitals

The penis and the testicles grow bigger in size.

illustration of increase in size of genitals during puberty in boys from age 9 to age 19 - Menstrupedia
5. Growth spurt

During puberty boys experience a rapid growth in height over a span of 2 to 3 years. This rapid growth in height is called growth spurt.

illustration of growth in height during puberty in boys from age 9 to age 19 - Menstrupedia
6. Ability to ejaculate

Boys become capable of ejaculating which is ejection of semen through the penis. The first ejaculation marks the attainment of sexual maturity in a boy's life.

illustration of ejaculation - Menstrupedia
References:
  1. Teenage growth and development: 11-14 Years, http://www.pamf.org
  2. Puberty and adolescence, http://www.nlm.nih.gov
  3. Reproductive anatomy and physiology, http://www.columbia.edu