Tanner stages start at TEN years old

Stage I:

• I is flat, as in flat chest;
• I is alone, as in no sexual hairs.

Stage II (2): stage II starts at 11 y/o (II look like 11)

• 2 balls (testicular enlargement)
• 2 hairs (pubic hairs now appearing)
• 2 breast buds form

Stage III (3): starts at 13 y/o

• If you rotate 3, it looks like small breasts (Breast mounds form);
• If you squiggle the III they look like curly+coarse pubic hair
• Increased penis length and size can be represented by: II --> III
  (your penis was thin II but now its thicker III)

Stage IV (4): starts at 14 y/o

• First imagine: The I in IV represents the thigh, and the V in IV looks like the mons pubis between your legs:
  MEANING: you have hair in mons pubis (V) but you have a border detaining the hair from growing into thighs.
• The V is pointy, as in now the breasts are pointy (raised areola or mound on mound)

Stage V (5): 15 y/o

• V has no borders detaining hair from growing into thighs (pubic hair + thigh hair)
• 5 fingers(as in hands) flattening the areolas when grabbing them (areola flatten at this stage and no more "mound on mound")

Pubertal gynecomastia is thought to be a physiological phenomenon, and is most commonly seen in midpuberty with Tanner stage 3–4 pubic hair and testicular volumes of 5 to 10 mL bilaterally.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3706045/

According to Goljan, men have boobs three times in their lives: when they're babies, when they're going through puberty, and when they're old. It's physiological/normal.

increased amount of estrogen compared to androgen activity is physiologic in puberty