If you're a complete beginner, lessons will be the way to go, regardless of your age. The most important reason is so that you have someone periodically checking up on you to make sure you're not forming potentially damaging habits that can make playing harder pieces more difficult or, worse, cause physical pain. Spend too much time playing on your own with no feedback from anyone else and you may think you're doing fine because you're playing the right notes, but you may be missing out on a lot of other things.