Thats not such a difficult question...we all went thru a process of handling our own craft, gaining confidence and knowing its limitations BEFORE we presume to venture into more dangerous/risky waters.
There is no set time line for this of course...no particular amount of hours logged at any point other than someone trying to get their license for the first time these days.
A large part of safety at sea is basic common sense...however knowing your own vessel is surely a prerequisite. Its as basic as knowing how much fuel you need, or carrying a spare main, knowing how to reef it solo etc etc...but it all becomes heightened when you put to sea on a mission to cross an ocean...SOLO.
I wont presume to think this particular bloke wasnt capable..might have been just a frustrated person that made a comment about his capabilites...BUT it simply begs the question what if he was asked a question about starting his engine and he didnt even know how he should sniff/blow the bilge, or how to check battery charge ? What if we found out his mainsail tore and he didnt know how to hoist a new one or use the foresail...you know what i'm saying yeah ?
We know 99 % of guys would know and learn their boats, check weather etc etc etc before attempting to fish a canyon at night that is say 25NM out to sea...but the guys that get rescued are often not just the unfortunate mech failures..shit happens to all of us.... but what about the 1% that ignore everything and just go ahead regardless. Brand new boat..."lets go".
Seems to me this is a very serious mission he was on...solo to NZ. Surely for THAT he should have an intimate knowledge of his vessel and emergency procedures. Question is ..what if he didnt ?...would you want him to not do it again until he knew what he was doing ? and maybe also send a message to others ?