We put DS1 into a bed a couple of months before DS2 was born. DS1 was 16 -17 months when we did it. We also use a bedrail although I'm not sure we still need it. We didn't have any problems with him going into a bed at that age. He chose his own linen and we sat on the bed for bedtime story for a couple of nights before moving him into the bed. We also made a big deal of the "big boy bed". Then on night 3 we asked him where he wanted to sleep and he said "bed". He went down without any fuss and slept through the night. From time to time since he has gone through phases which last a week or so, where he will get out a couple of times before staying put. And one phase lasted 3 or 4 weeks and just finished, where he would get out of bed during his day time sleep. But we are back on track now, and overall the transition was easy.