Baba Basra 156a - Being Machzik as a Gadol in Retrospect

R. Akiva Eiger (Teshuvos 7) discusses a sofer who had his son who was just about 16 assist him in the writing tefillin. Being that the son was never checked by witnesses to verify that he was physically an adult, R. Akiva Eiger wrote that the assumption of Rava in Nida 46 to assume he is an adult based on age would not work for a d'oraysa issue such as tefillin and Mezuzah.

However, R. Akiva Eiger writes that if they would check him today and find that he indeed has halachically reached physical maturity, all the tefillin that he wrote from when he was 13 would be kasher. The source of this ruling is Tosafos (d.h. bodkin) who writes at the end that if we would check a girl a few weeks or months after her 12th birthday and found simanim, even if beforehand she had accepted kiddushin from Reuven and then from Shimon, we are only concerend about the kiddushin of Reuven, not the kiddushin of Shimon. We don't have to be concerned that she got simanim in between the kiddushin of Reuven and Shimon, because "now she already reached gadlus, so we assume she was a gadola for a long time before". R. Akvia Eiger undertands that to mean that since now we know she is definitely a gadola, we can use the chazaka of Rava to tell us that he probably became a gadola from her 12the birthday. Therefore, this son of the sofer is also assumed to have been a gadol from his 13th birthday.

R. Akiva Eiger questions this pesak based on the Ramban that we mentioned yesterday who says that the story in b'nei berak is only if the boy died immediately after selling property, which implies that if he sold the property and then died 2 weeks later, even if we dig him up and find that he was a gadol when he died, we are concerned that he wasn't a gadol at the time of the sale (r. akiva eiger also points out that the rosh disagrees with the ramban). Clearly the Ramban holds that we don't say since he died as a gadol ,we are machzik him as a gadol from the moment he reached 13? But, R. Akiva Eiger explains that even the Ramban would agree in our case that we are machzik the son of the sofer as a gadol from when he was 13. The Ramban is only machmir in monetary issues, that we aren't entitled to take away money from the inheritors based on that assumption.