Some people in the Bible did retire at a certain age; the Levites (who assisted in the Temple ceremonies) had to retire at the age of 50 (see Numbers 8:25). Farmers and other laborers, however, apparently worked as long as they could.
It wasn't necessarily wrong for you to retire -- but what was wrong was failing to plan how you'd spend your retirement. I don't blame you; most people, I've found, don't give much thought to it. They look forward to not working; they have their financial plans in place; they even may have a hobby they want to pursue. But that's as far as they get in their planning, and -- like you -- they end up bored. Perhaps your experience will encourage others who are nearing retirement to give it more thought -- and prayer.
I added "and prayer" to that sentence deliberately -- because God knows all about your situation, and He has a plan for these years. Why not seek it? Perhaps he wants you to explore a part-time job, or take some classes you'll enjoy.
But God also wants to use you to help others, now that you have the time. What opportunities does your church offer? What mission projects could you join? Don't live just for yourself during these years; you'll keep getting bored. Instead live for Christ, and ask Him to use you. The Bible says, "Whatever you do, work at it with all your heart, as working for the Lord" (Colossians 3:23).