If I live with my 7 month old son and he shares a room with me, how old does he have to be when he needs his own room?

There is not a law in Texas that sets out when a child is to get their own room.  Sometimes, finances are strapped which naturally limit resources.  However, as the child starts to hit the Jr. High years, courts in custody disputes do tend to frown on children not having their own "space."  If you get into a custody dispute with the other parent, then the lack of space exclusively for the child (even at his current age) will be a factor the court will take into consideration in deciding custody.  If funds are strapped, consider a couple of different things to give your son some identifiable "space" to prevent this type of issue.  First, consider giving the child the room, but sharing a closet with the child.  Let your son sleep in the room and arrange for a fold-away bed for yourself in the living room.  Many parents have had to convert the living area into rotating bedrooms in this economy. (Do not kick your son to the couch-- your ex- will have even more ammo if your son goes for a visit with news that he is required to sleep on the court.  Courts don't care if you sleep on the court-- but will if the child does.)  A second option is to partition the room.  A sheet or a divider can give the child a clear and identifiable space for toys, clothes, and school supplies.  It can also serve as a private changing area.   Again, this is not a requirement, but being sensitive to this issue will help you prevent an expensive and emotional custody suit later.