D&C 20

 As the Church was being organized, we learn that - 

"...Joseph Smith, Jun., who was called of God, and ordained an apostle of Jesus Christ, to be the first elder of this church;

3 And to Oliver Cowdery, who was also called of God, an apostle of Jesus Christ, to be the second elder of this church, and ordained under his hand..."  (Doctrine and Covenants 20:2–3)

And that - 

"The duty of the elders, priests, teachers, deacons, and members of the church of Christ—An apostle is an elder, and it is his calling to baptize;

39 And to ordain other elders, priests, teachers, and deacons..."  (Doctrine and Covenants 20:38–39)

The title elder is the word used in reference to the higher priesthood.  It seems apparent to me that the use of "elder" in this section is in reference to one that holds the Melchizedek priesthood.  What seems interesting to me is the reference to order being that the Prophet is the first elder in the Church.