Can't tell you what it's like, that would spoil the surprise.
Advice: take good care of your teeth and skin. Avoid impacts, broken bones or serious strain injury. Minor injury you receive when young will become more aches and pains as you age. Keep your back strong and straight. Lift with your legs. Wear hats and long sleeved shirts when your going to be in the sun for a long time. Treat your friendships and romances seriously, the embarrassments of your mistakes will be with you for a long time. Fill your memory with as many beautiful things as you can, it makes reminiscing more enjoyable. Don't talk so much!