I don't know for sure(i cant find out anywhere), but I heard that Maxim Kozhevnikov was a young adult when he started(I heard 20 I think). He went on to be in the world pro final. Ether way, there are a few world champions that have had a late start, and tons of couples that have had remarkable improvements in short time periods. I am not sure exactly how old Jonathan Wilkins was when he retired(ballroom dancers are not always open about things like age), but I think it was early forties. Really I would like to say that age doesn't matter but even at your age it's hard to say it's impossible. Can anyone really say that twenty years is not enough time to become a world champion?
The thing is, reviewing past world champions views, most of them didn't set out to be a world champion. It's about wanting to become skillful. If you want to be an awesome ballroom dancer, go and become awesome. Achieving the skill is success. The result is external. There are so many reasons why seeking becoming a champion doesn't make sense. If you live by the judges mark then your life is theirs, not your own. You don't have to be good to be a "winner". You only have to be "better" than everyone else. And if that is what you seek then again your life is not your own, it belongs to those who you desire to conquer. You don't want to HAVE to practice to be better than others. You should want to practice because you love dancing.
If you do decide that ballroom dancing is something that you want to pursue in your life the most important thing you need is a mentor, a coach. Not someone who just gives you lessons but someone who teaches you how to pursue ballroom; what competitions to dance, what lessons to take, what you can do to have a good relationship with your partner. This process can take a lifetime if you are wandering about. It takes careful guidance to learn these skills. Don't become discouraged. You will become great if you desire. Good luck on the journey and don't forget to keep the desire alive.