He and all his family were devout and God-fearing…He will bring you a message through which you and all your household will be saved.' (Acts 10:2, 11:14 NIV)
They replied, "Believe in the Lord Jesus, and you will be saved—you and your household." Then they spoke the word of the Lord to him and to all the others in his house…then immediately he and all his family were baptized. (Acts 16:31-33 NIV)
One of them was Lydia…she accepted what Paul was saying. She was baptized along with other members of her household, and she asked us to be her guests…Paul and Silas then returned to the home of Lydia, where they met with the believers and encouraged them once more before leaving town. (Acts 16:14-15, 40 NLT)
Crispus, the synagogue ruler, and his entire household believed in the Lord; and many of the Corinthians who heard him believed and were baptized. (Acts 18:8 NIV)
The simple answer is, "We don't know." I once asked my Seminary professor how old a person should be before being baptized and his answer was simply, "That sounds like a good topic for an advanced degree student to study for his thesis paper." I chose a different topic.
However, I did do study on this topic because of it's practical application in everyday life. Here's what I've found.
1) There are no examples of infant baptisms in Scripture.
2) There are examples of family baptisms. In them, the family members were old enough to be "devout and God-fearing," "Believe in the Lord Jesus," "encourage" the believers, and "believed in the Lord." In other words, they were old enough to make decisions and do things, but we have no specific age.
3) For Jewish believers, there was already an age of accountability that cannot be found in the Bible. We know that in the first century (Jesus' days) the Talmud (Jewish teachings) state that for boys, "At age 13, one becomes subject to the commandments." Girls have the same at age 12. (I guess they really are more mature than us guys.)
The idea of infant baptism didn't appear until a little later in church history and was directly tied to the doctrine of Original Sin. This teaching states a specific interpretation that we have the sin of Adam and Eve placed on our souls at birth. Since we have sin "on" us, as the thought goes, we cannot go to heaven if we die before being baptized. Worried parents, then, would want their babies baptized so they can go to heaven.
Reading the writings of early church fathers, though, we find that there was no agreement on ANY of this. Some teachers believed children were born innocent - no original sin. Others believed they were born with the sin of Adam. They debated this in their writings for hundreds of years. It wasn't until Augustine of Hippo (354-430 AD) that the teaching of original sin was made official in the church. To give us Americans a point of reference, the United States isn't even 400 years old yet. They argued over what was true in this area for longer than our Country has been in existence!
To make things worse, there was also no agreement over what would happen to the babies even if they did have original sin on their souls. Some said they would go to heaven anyway because it was not their own sin. Others said they would need to perish in the fires of hell (creating fear for us parents). Still others came up with another "place" these children would go. The place was named "limbo." Limbo was a place separated from God, but with no pain or suffering. The Roman Catholic church finally settled on this teaching as being the place where infant "innocents" went...until recently. Now, that teaching has been revoked officially by Pope