dont worry abuot the age, insist on finding one with a near perfect condition and you'll be fine. remember the trick for buying an old mercedes is to choose based on condition not color/accessories.
i have an 1974 Stroke 8 and it rides a hell lot better than my dad's 2005 Toyota sedan.

ps: ask the owner of what type of oil he use for the car, if it's mobil 1 then it's probably a well maintained example.

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w202 c200 malachite green
w115 200 green