Hello, Thanks for letting us know your health concern. I have gone through the query and would like to offer you some information. Some features indicate the onset of puberty like- growth of hair in underarms and on the mons pubis, development of the breast tissue, increase in discharge from the vagina indicating the activity of the hormones, weight gain in some children while some have a growth spurt etc. The measurement of hormones also helps to detect the onset. Finally, family history plays an important part. Hope this helps.