Use the adjective advanced to describe something that's ahead, especially in terms of growth or development. Your plans to build the world's best tree house are at an advanced stage if you're nearly ready to add a roof and invite your friends to visit.
Things are advanced when they happen early or are ahead of the curve or above average. Your advanced reading ability in elementary school might have had your teachers scrambling to keep you interested, and if a scientist's cancer vaccine is at an advanced stage, it's nearly ready to be tested on people. Advanced comes from the verb advance, which comes from the Old French avancier, "move forward," from a Late Latin root word, abante, "from before."
adj ahead in development; complex or intricate
adj farther along in physical or mental development
characterized by or characteristic of exceptionally early development or maturity (especially in mental aptitude)
adj at a higher level in training or knowledge or skill
greater than normal in degree or intensity or amount