There does not seem to be a particular age at which people are sent to the House of the Old in 
The Giver. Once people's children have grown and are out of the house, they are moved to the place of Childless Adults, and there they remain, "As long as they're still working and contributing to the community" (124).  The implication is that when people are no longer able to be productive, they are sent to the House of the Old.  The House of the Old resembles what we think of as a nursing home. The residents are physically cared for, for example, bathed by volunteers like Jonas and Fiona, and it seems that each resident has a room to him or herself, but there are common areas where people can socialize or participate in activities such as crafts.  In some ways the Old are treated like children, for example, as the discipline wand is used on them as it is used on children. The Old are cared for in the House of the Old until they are Released. It is not clear that there is a particular age for this. The Elders no doubt are the people who decide at what point people are no longer productive and needed to be moved to the House of the Old, as they probably also decide at what point people must be Released.