Hi,
"To get the most accurate measurements for an individual's penis size, it has been recommended that several measurements be taken at different times, preferably with different erections on different days. Then average these figures together. This is to account for what may be natural variability in size due to factors such as arousal level, time of day, room temperature, frequency of sexual activity, and unreliability of the measurement methods.[2][3]
Length
The length can be measured with the subject standing and the penis held parallel to the floor. The penis is measured along the top, from the base to the tip. Results are inaccurate if the measurement is taken along the underside of the penis, or if the subject is seated or prone.[2]
Circumference
Penis girth is the measurement of the circumference of the completely erect penis. It is variously quoted as an average of three measurements: just below the glans penis, in the middle of the shaft, and at the base."
en.wikipedia.org/wiki/Penis_size
"Sequence of Pubertal Events in Males
Event Average Age in Years
Initial testicular growth 11 ¾
Early growth of pubic hair 12
Enlargement of penis begins 13
Temporary breast development 13
Voice cracking begins 13
Growth spurt 13 ½
Hair in armpits 14
Wet dreams 14
Adult voice attained 15
Moustache begins to appear 15
Whiskers appear 16"
www.massgeneral.org/children/adolescenthealth/articles/aa_puberty.aspx
You seem to be developing according to the normal average.
Development in secondary sexual features in the male continue until age 21.
It is normal to wonder whether you are developing normally, but if you feel you have serious deficits in certain areas, it would be best to discuss this further with your physician who can advise hormonal evaluations and referral to an endocrinologist based mon any abnormal results.
I do not think you need any medical attention in this regard.
Do keep us posted on your doubts and progress.
Regards