You can start wearing your baby right from birth.For newborns and infants using a sling is advisable as the infant cannot support its neck and head. Once the neck muscles develop and he/she cand support his/her head you can move onto using baby carriers.Keep in mind while using carriers that the knees should be higher than the bottom and legs evenly spread out.Do not leave the legs dangling.Try and avoid forward facing carriers as they do not give proper spine and back support to your child.
You can babywear from birth. Babies at different stage has different needs and their physical development varies. Example for newborns you need to make sure there is adequate support for neck.