Best: It feels like a fresh start, somehow. It also just 'sounds' important in a way because it is a round number.
Worst: Even if you are completely fine with the age, and are aware that age is just a number and your outlook on life is what is important, others tend to make a huge ordeal out of it all, and expect you to just sit down and rust because you are now ancient.
Living near water (lake, canal, sea..)