I think you raise four key questions we should ask ourselves daily: Compared to whom? Compared to what period of your life? With what habits? And for what purpose? It's all well and good to adopt a proactive and optimistic attitude, but we're still social animals, and typically, if the environment is hostile, we react poorly or adapt negatively. Perhaps after your four excellent questions, it's necessary to include a fifth: How do I do it?
And I think no matter what the goal, the answer is pretty easy to start formulating. What have other people done to achieve similar?