Yes, correct posture is very important so that you don't clamp off your blood supply. Your mother (or grandmother, or aunt, or older sister, or doctor) can show you the correct posture.
If you consider a routine before age 18, you will very likely do irreversible damage and actually grow smaller! It is very serious. See my message above.
If you consider a routine before age 18, you will very likely do irreversible damage and actually grow smaller! It is very serious. See my message above.