There’s a saying that goes: the best time to start was 10 years ago. The next best time is right now. That applies to any project, including taking up judo!
Sure, it would have been better if you started when you were twelve and trained continuously with the best coaches and sensei, traveled the world competing in all the top tournaments, and became an Olympic champion at age 25. And if you’re twelve years old right now, that path is still available to you! But if you’re already 25, or 35, or 45, judo is still a great choice to get in shape and learn useful self defense skills. It’s also a ton of fun learning how to make people fall down.