Set yourself a challenge for the year. I turned forty in May, decided I wanted to be in Africa on my birthday, and to run a marathon in the year. Had a brilliant time in Zambia and Botswana, went white water rafting, and on the horseback safari, went swimming on my horse. Also got chased by lions whilst on the horse, which almost shortened my life expectancy...
Got back from New York this weekend, having run the New York marathon, which is the most fabulous running race. Had an absolute ball running alongside the most enthusiastic crowd you can ever imagine.
Anyway, as you get older, you'll probably find as I do that you can't instantly remember how old you are. You can always do what I do, which is work in a hospital. Most of my patients are in their seventies and eighties, and it really changes your perspective on age.
Enjoy life, you only get one shot at it.