Buyers build a five-year capital plan during diligence and reduce their offer by what the plant will need. Documenting what has already been spent and maintained offsets most of the automatic discount.
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Age alone is not the issue; capability and reliability are. A twenty-year-old machine that holds tolerance, runs daily, and has documented maintenance is a working asset. The same machine with no maintenance records and intermittent downtime is a liability on a buyer's schedule. The most useful preparation is a current equipment list with year, hours or cycles, control generation, and maintenance history, plus an honest note on what will need replacement and when. Sellers sometimes ask whether to buy a new machine before selling. The answer is usually no unless it is already justified by the work, because the purchase rarely returns its cost in valuation, while the documentation costs nothing and does.