Golf clubs are designed to last a lifetime, and there is no evidence that they deteriorate over time. Pure blade designs have remained largely unchanged for years, as there is only so much you can do with a solid piece of metal shaped like an iron. The biggest difference between vintage and modern clubs is that vintage clubs tend to have the center of gravity closer to the heel and a more square leading edge. If you can consistently hit the sweet spot, there is no reason why you can't play vintage clubs.
It is possible to have your irons reconditioned, and it is best to do this through the original manufacturer if that is an option. This will ensure that the clubs continue to function as they should. Golf technology changes rapidly, so irons older than five years are likely to be outdated and not perform as well as the latest models. However, if you are an amateur golfer who only plays golf on the weekends, it will be a long time before your irons start to lose distance.
Wrought irons use softer steel than cast irons, but unless you play golf several times a week, the average player won't notice much difference in terms of longevity. If you are not getting results with your current set of clubs, it may be wise to consider upgrading them. You can also try out new sets through the U-Try program on GlobalGolf before making a purchase decision. If you find that your swing hasn't changed but your distance has decreased, it could be something happening with the clubs themselves.
It depends on how often you play and how well you take care of your clubs as to how long a standard set of clubs will last. Buying new clubs can be expensive, but you can usually get great deals and open up more options if you are on a budget.