Found this definition of what 'retro' is. Thought it was quite a good explanation because it takes into consideration of how it becomes modern and that our mixed up world find old fashioned things fashionable.
"A retro product is a modern product that draws on the past for inspiration. Some retro products are replicas or re-issues of old favourites; others are new designs, but with style or detail touches that suggest an earlier period. Most perform in exactly the same way as their modern looking equivalents, but look old fashioned, and in our mixed up view of the world are more fashionable."
What makes a great retro product?
"A retro product needs to capture enough of the essence of the original form to inspire feelings of nostalgia for the original. It can be a copy of the original, very close to the original design, or retro products can capture the essence of the original, but offer something new."