Can a member of an SMSF be less than 18 years old?

Yes, a member can be under 18 in a super fund.

If the under-age member does not have a nominated legal personal representative, a parent or guardian must act as trustee of the fund on their behalf.

Where the SMSF has a corporate trustee, a parent or guardian is allowed to be a director of the trustee company in place of the underage member.