When they can demonstrate above ground that they can put
On an srt kit, decend safely including putting in a hard lock, can prussik and change over to come back down, can pass rebelays, deviations and knots. Itd be a good idea to ensure a novice is partnered with somebody experienced to check that they are for example loading the stop correctly etc or can talk them through should they get stuck and most importanty that they are confident they are ready.
Hope this helps of course there will be people with probably better advise buts thats what i would go on, make sure they get plenty of above ground training with experienced club members