So right now I'd like to talk about the highest leadership in the LDS Church: The First Presidency and the Quorum of the Twelve, and the way LDS presidential succession works.
1) Russell M Nelson: Apostle since 1984, Nelson was formerly a heart doctor, and has been present at many firsts in heart surgery. He even performed heart surgery on an apostle that later became church president. Nelson is currently 92 years old, and appears to be in relatively good shape for that age. If he outlives Monson (likely), he will become the next church president. He's had a few socially conservative talks, but his focus is usually on healing and learning.
2) Dallin H Oaks: Apostle since 1984, Utah Supreme Court Judge from 1980 to 1984, and President of BYU from 1971 to 1980. Oaks is probably one of the more conservative apostles, and often has strong "culture warrior" talks focusing on religious liberty and the right of the church to speak its own opinion. Mormon liberals don't tend to like him. He is 84 years old and in good health. He tends to give his sermons like a lawyer laying out a case. Despite being ordained at the same time as Nelson, Oaks is younger than Nelson, so is junior to him.
Excellent recap of the Church leadership.
But to my understanding and study, age has nothing to do with seniority in the Quorum of the Twelve Apostles, but everything to do with date and time of ordination to the Quorum.
So the reason Nelson is senior to Oaks in the quorum is because Nelson was ordained to the quorum in April 1984 and Oaks was ordained to the quorum in May 1984. Therefore, due to the fact that Nelson was ordained before Oaks, Nelson is senior to Oaks in the quorum.
It has nothing to do with the fact that Nelson is older than Oaks, but simply because Nelson was ordained before Oaks.
If two or more new Apostles are ordained on the same day, they would take their places in seniority in the quorum in the order in which they were ordained.
