What is a term for someone who doesn't know what they haven't experienced?

You may want to use oblivious.

If you don't want negative connotations, perhaps simply describe them as unaware:

not aware or conscious; unconscious: to be unaware of any change.

Other possibilities include uninformed or incognizant.

tabula rasa

blank slate

(for the present context) the OED defines this term as follows:

an absence of preconceived ideas or predetermined goals; a clean slate:

the team did not have complete freedom and a tabula rasa from which to work

a mind not yet affected by experiences, impressions, etc.

a young mind not yet affected by experience

the mind in its hypothetical primary blank or empty state before receiving outside impressions

something existing in its original pristine state

cultural definition Something new, fresh, unmarked, or uninfluenced. Tabula rasa is Latin for “blank slate.”

Thus you could say: My mate is new to this corporate world of jealousy and hostility - he's a tabula rasa.

Example sentences from Collin's dictionary:

"But you don't start with a tabula rasa (clean slate), you have to deal with society as it is, and try to make constructive progress. TIMES, SUNDAY TIMES (2001)

It was on this tabula rasa , Picasso believed, that a new art form could originate. TIMES, SUNDAY TIMES (2002)

Porn, on the other hand, is a tabula rasa as far as greatness is concerned. Victoria Coren, Charlie Skelton ONCE MORE, WITH FEELING: HOW WE TRIED TO MAKE THE GREATEST PORN FILM EVER (2002)

With someone new, you're a tabula rasa , which has its charms for those who enjoy reinventing themselves. GLOBE AND MAIL (2003)

Since all your examples refer to the lack of a negative experience which can be considered positive (well, not entirely, there a negative experiences you cannot avoid forever, e.g. death), translations of the German word unverdorben might fit quite well:

• pristine
• unspoiled / unspoilt
• ingenuous (or innocent, as Edward Ashworth suggested)
• untainted
• uninjured