African Violets can be very long-lived if well cared for. They can easily live 30yrs+. I have a few that are about 15 yrs myself. As for repotting, I've been lazy and have kept some plants in the same pot for as long as 2 years. After that I've been known chop the plant off at the soil line leaving a long neck on the plant, cleaning up the pot, putting fresh potting mix in it, and putting the plant back in the same pot. After about 3 weeks it should be anchored and you should be seeing new growth.

African violets certainly are long-lived, and although some people can stretch repotting out for a long time, it's recommended that it be done every 6 months or so. This keeps long, bare stems (necks) from developing, and it only takes a couple minutes per plant. After 6 months the peat in the potting mix can begin to break down, and this causes problems with the plant being able to absorb nutrients properly. I'm including a tutorial on how to repot from the Violet Barn in a link below.

Mark