When does a believer become an heir with the Father and the Son?

Les explains that in the Roman and Greek culture, a child born to the husband and wife was put under tutors, educated and trained to come in at an equal level with the father, and when reaching that point went through the rites of adoption. The Hebrew equivalent was the Bar Mitzvah at age 14, but that was not the same category because Romans and Greeks were in the secular world preparing a co-worker in the business. Paul teaches that the moment we become a believer, we do not go through years of tutoring and training; we are immediately placed as an heir with the Father and the Son. This was the predestinated position for a believer, not to heaven or hell, but to be with Christ from day one as a joint heir in the process of the adoption. He also says in Ephesians 1:11 that we have obtained an inheritance and are joint heirs with Christ, meaning there are other parties, and in the secular economy, if the other half passes off the scene, the heir ends up with it.