The age of a writing instrument cannot be worked out from the ident number. It denotes the model and the version and nothing else, which makes it most comparable to an order number in a catalogue; the same number may have been used for years on end for a model in continuous production. Placing a pen in time takes at least the serial number, which on more recent instruments is engraved into the clip or on the cap ring.
Even the serial number, though, is of limited help to collectors, since the code is not publicly documented and cannot be decoded from outside. Anyone who wants to know the date of manufacture for certain has to approach Montblanc directly with the number; the manufacturer can trace it in its records. Quite apart from that, dating by features such as the nib stamping, the engraving of the cap ring, the material of the body, the filling system and the packaging will usually narrow things down to a few years, which is as a rule quite enough for a purchasing decision. On a Solitaire Vermeil, for instance, the hallmarks and the finish of the fittings will at least establish the period of manufacture.