"Should I be worried that it's so old" - not to worry about the age, as most everything in or on a boat is replaceable to good-as-new, the only question is cost. What have the prior owners gotten to versus what still calls for attention? There are no flat guidelines on this subject, it is all judgement. Don't assume that because the price is very low, or that the prior owners have sent $XXX,000 on upgrades that the financial risk is low. Think of the analogy where buying a car in parts can cost 5-10 much buying the car itself, the same is be true of boats, but the parts cost 5-10 times as much!
A suggested formula might be:
purchase cost + 2*cost of possible repairs/replacements < needs-no-work market value
Don't be dreamy-eyed about the cost of possible repairs/replacements, these should be estimated based on work lists from demanding boat and engine surveys, supported by written yard estimates. You will still end iup with surprises and overruns, thus the times 2.
If the particular boat doesn't pass the financial test move on. If you are in a hurry, pay the premium price for the needs-no-work version, buying a properly maintained and upgraded boat is the low-risk and low-cost way to get one. Buying the fixer-up or needs-work boat involves high risks of getting financially hosed, and even then to decide to dump the remainder onto the next guy.......