He should be just fine to answer NO to the question concerning a misdemeanor offense of domestic violence. The definition of that is contained in 18 USC 921 and if the offense occured as a minor and is sealed it 99% chance does not meet the definition of 18 USC 921:
US CODE: Title 18,921. Definitions
(33)
(A) Except as provided in subparagraph (C),[2] the term “misdemeanor crime of domestic violence” means an offense that—
(i) is a misdemeanor under Federal, State, or Tribal [3] law; and
(ii) has, as an element, the use or attempted use of physical force, or the threatened use of a deadly weapon, committed by a current or former spouse, parent, or guardian of the victim, by a person with whom the victim shares a child in common, by a person who is cohabiting with or has cohabited with the victim as a spouse, parent, or guardian, or by a person similarly situated to a spouse, parent, or guardian of the victim.
(B)
(i) A person shall not be considered to have been convicted of such an offense for purposes of this chapter, unless—
(I) the person was represented by counsel in the case, or knowingly and intelligently waived the right to counsel in the case; and
(II) in the case of a prosecution for an offense described in this paragraph for which a person was entitled to a jury trial in the jurisdiction in which the case was tried, either
(aa) the case was tried by a jury, or
(bb) the person knowingly and intelligently waived the right to have the case tried by a jury, by guilty plea or otherwise.
(ii) A person shall not be considered to have been convicted of such an offense for purposes of this chapter if the conviction has been expunged or set aside, or is an offense for which the person has been pardoned or has had civil rights restored (if the law of the applicable jurisdiction provides for the loss of civil rights under such an offense) unless the pardon, expungement, or restoration of civil rights expressly provides that the person may not ship, transport, possess, or receive firearms.
