We converted DS's crib to a toddler bed at 17 months because he kept climbing out of the crib. I wanted to wait until later to make the change but since he was climbing out I didn't have much choice. The transition wasn't that bad although most nights he falls asleep in the rocking chair in his room and I have to move him back to his bed.
We just made sure to extra baby-proof his room and took out most of the toys and just left board books and stuffed animals so he wouldn't get too distracted when he was trying to fall asleep. Otherwise he would just stay awake playing all night.