1. You can arrive at RMAS at 29 in order to commission when you are 30, but RMAS are encouraging people to arrive before they are 27;
2. Regiments have an ideal in their minds that pl comds are young and have little or no baggage. Some regiments will not look at people who are older than average but other regiments will select regardless of age.
Current RMAS average age is 23.
There is no formal policy - just general practice which is different from regt to regt.