when is a good age to let baby sleep on their own bed?

If you mean in the same room as you, you can let baby to sleep on his own crib since newborns. If you are referring to toddler bed (in the same room as you), you can switch after he/she turns 1 year old. However, it is recommended to use bed safety guards to prevent from falling down. If you are intending to let your baby sleep in his/her own bed but in a separate room, this will depend on how ready is your child. For me, I prefer to stay close to my kids when they are young (below 3 years old) and save the troubles I need to travel between rooms at mid-night. My daugther transferred to her own room and bed happily after she turns 5 years old. For my second baby, he is more ready to sleep on his own bed and room at the age of 2.

It's been said that it's best to let babies sleep in the same room with the parents for the first 6 months. You can put your newborn in a cot or Moses basket beside the bed. Babies have trouble settling themselves and need their parents to comfort them for the first 2 months. When ready to move your baby from a bedside cot to a separate cot, try to do it on a gradual basis. Start by having the cot near your bed, then, if you have the space, move the cot further away. When you do move baby to his or her own room, remember to have a baby monitor. http://www.babycentre.co.uk/a536773/when-can-i-let-my-baby-sleep-alone

thanks