Sleeping with mom and dad.
We had our son sleep with us in our bed for his first 3 months and then had him sleep in his crib from then on. Occasionally, he'll take a nap in our bed still though. He transitioned very easily, he had no problem with his crib. I would say for taking naps, no age is too old for me. For sleeping through the night, I would want to make it stop by 3 or 4. :)