The boy sized Oyster Perpetual. That can't be it with a set of diamonds sitting at 6 o'clock! Yes but a Datejust 31 can too be had without shiny rocks. That being said, it is a hard sell to men unless both a Datejust 36 and OP 34 are on the bigger side for one, which is unlikely. So the DJ 31 is likely reserved for the ladies.
Finishing for an 'entry level' Rolex
Desirability of the crown watch