About 40% of Royal Navy Engineering Officers joined as Ratings.
There are about 800 Royal Marine Officers, 85% of whom have a degree.
There are about 6500 Royal Marine Other Ranks (RMOR), 40% qualified educationally for Officer.
There are usually fewer than 4 Corps Commissions a year. (promotion from RMOR under age 26)
Each RMOR Recruit Troop (55 men) averages 3+ graduates, the most I recall is 17 in one troop.
Those joining <19 or >30 have half the success rate of those entering between ages 19-23.