Yes, its polite to use. and its not old. its normally used nowadays.

ご存知＝gozonji This word is often used in business occasion but not used in informal occasion. If you use this in off-work or casual party , you won't be liked , I'd say . 存じる is the Kenjougo of "know" (this word is a kind of respectful phrase and this word gives an impression that "speaker is in the lower position than the audience in conversation" and sounds like polite for Japanese. In Japan , people need to use the Kenjougo to express their own affair or matter in business occasion while people need to use the Sonkeigo to express the clients or worth people to be respected. If you want to know the word further , you should study the difference between Sonkeigo and Kenjougo in Japanese grammartical book.