At any age, explore the variety of websites that offer instruction in math and games that allow you to practice in both fun and informative ways. One popular website is Math.com, which aims to provide "a greater love of mathematics, both for its beauty and its power to help solve everyday problems."
Research which schools offer online degrees in mathematics if a degree in math is attractive to you. While some schools offer only selective online courses and require some instruction at actual brick and mortar campuses, universities such as the University of Illinois at Springfield offer "an opportunity to obtain the Bachelor of Arts degree in Mathematical Science" entirely over the Internet.
Research the requirements and prerequisites for studying at these institutions once you have decided upon a group of schools. Most require some form of standardized testing and a high school diploma or its equivalent.