In all honesty if your garage door is still in good working order then there is no “right” time to replace it. With that being said an older garage door can really date your home making it look a little older and more run down than the rest of the homes in your neighborhood. Garage door manufacturers are also coming out with new garage door technologies every 5-10 years that are great improvements in safety and functionality, so it can greatly benefit you to upgrade your door once every 10 years.
At the end of the day if your door is working great, then keep on. But a new garage door can make your whole home look new and it can save you money in electricity because it will operate in a much more cost efficient way!