would be better to go to a reliable Christian commentary and learn the history of the practice that Paul mentions in 1 Cor while defending the resurrection of the dead. I was taught that if someone had died shortly after giving their life to Christ, that is when the baptism was done by proxy.
My brothers and I became Christians one day in Mar ‘61. My oldest brother died in Nam but I don’t believe he was ever baptized. In 61 he would have been around 8 1/2. I’ve thought about the proxy thing, but never did any real research into it.
Start research here: “baptize+dead”