Most kittens are between 6 and 8 weeks when you bring them home, which is a good age to start a new life. At this age they are fully weaned, eating proper food and have learnt the basics of clean habits. Kittens that are very young may not thrive properly.
Always get your kitten from a reputable breeder or pet store and make sure it has had all its necessary inoculations. Check local government regulations regarding registration. Take your kitten to your own veterinarian to have a complete health check and find out what other vaccinations and health care is needed.