As long as it takes, I`ve spent 7 years with two children in bed with me and my husband and all I got was a quarter of the bed for 7 years! talk about a lack of sleep for all of those years, but I had my daughter sleep with me until I had her little brother I think that she was 3 years old when I moved her to her own bed, then I slept with my son until he was 4 before I moved him to his own bed so combined that was many years of sleepless nights for me but they adjusted well. Now that I finally have the bed all to ourselves (me and my husand) the cats have taken over! Just as long as I can stretch out my legs I`m happy! After I moved my kids to their own beds I would still continue to lay with them and sing them lullabyes to this day until they fell asleep or tuck them in and kiss them on the forehead and leave the room, if they get up I ignore them and put them back to bed until they give up and fall asleep, Good luck dad it is a labor of love and I commend you!
7 or 8 depending on the kid is a good age I think
I have raised three.
I will say this. The earlier you get them established into a regular bedtime routine in their own beds, the better it will be you and more importantly - for them. (Providing they are past the early baby waking every 2-3hrs phase.)