Bava Batra

thus said R. Johanan to R. Simeon b. Lakish: According to my interpretation that  proof [is produced] through the attestation of the deed, one can well understand how it was possible for the buyers to seize  the property.  according to you, however, since you maintain [that] proof [is to be produced] through [the evidence of] witnesses, how was it possible for the buyers to seize  the property?  — He replied to him: In the case of a protest on the part of members of the family I agree with you that it is no [legal] protest; [for] what do they plead? [That] he was a minor! [But] it is an established fact [that[ witnesses do not sign a deed unless [they know that] he was of age. It was stated: At what age  [may] a minor sell his [deceased] father's estate? — Raba said in the name of R. Nahman: [When he is] eighteen years of age. And R. Huna b. Hinena said in the name of R. Nahman: [When] twenty years of age. R. Zera raised an objection: It once happened at Bene-Berak that a person sold his father's estate, and died. The members of his family. thereupon.  protested. asserting [that] he was a minor at the time of [his] death. They came [to] R. Akiba and asked whether the body might be examined. He replied to them: You are not permitted to dishonour him; and, furthermore, [the] signs [of maturity] usually undergo a change after death.  [Now], according to him who said, 'Eighteen years of age'.