How long did you exclusively breastfeed for?

Most of my friends try to breastfeed exclusively for at least till their babies are one-year old. They would then introduce regular milk. A few had to stop after six months as they have returned to work and it was not easy for them to pump and had a hard time trying to keep up with the supply. There are some who are still breastfeeding (children are beyond 18 months now) and would try to continue till their little ones indicate that they want to stop.