In the monastic community, senior or junior does not refer to older or younger in age, but the number of years since ordination. The title “Thera” (Elder) is conferred on Bhikkhus 10 years after ordination, and “MahaThera” 20 years after ordination. Juniors should salute seniors. Seniors precede juniors while walking along. As to sitting, the upper seats to the juniors, and juniors should not sit unless asked to sit by seniors. So in the southern Buddhist countries, the inquiries about ordination time are necessary for monks when they meet each other. Normally when ordinary bhikkhus meet a MahaThera, they are required to take off their shoes, and expose their right shoulders, and then make salutation. (From Essentials of Buddhism: Questions and Answers)