According to a Forbes article, the average lifespan of a website is 2 years and 7 months, although this timeframe can vary depending on the industry and other factors.
However, it's important to note that a website's lifespan is not the same as the optimal time frame for bringing the best results.
The lifespan of a website refers to how long it remains functional and up-to-date, while the optimal time frame for bringing the best results depends on a variety of factors, including the business's goals, industry, and target audience.
Factors such as changes in technology, design trends, and user behavior can all impact the lifespan of a website.
To ensure a website continues to bring the best results, it's important to regularly update and refresh the site's design, content, and functionality to meet the changing needs of users and the business.
Ultimately, the optimal time frame for a website design to bring the best results will vary depending on the specific business and its goals.
It's important to regularly evaluate the website's performance and make updates as needed to ensure it continues to deliver the desired results.
As a business owner or marketing director you should ask your staff and other contacts if your current website accurately reflects your company and that you feel very confident that no improvements need to be made.
Note though that security concerns are often one of the main reason to update the core software and at that time it can be quite easy to update the styling and change the navigation structure as well.
It's always worthwhile to have a chat with your website company and get their input. If you trust their judgement they should offer you unbiased advice and not try and sell you something you don't need.