I took up tennis a year ago, then aged 18. I'd certainly rank it as one of the best decisions of my life. Of the 12 months I've been playing I think I've missed 4 months through injury and have still managed to reach a decent level.
As has already been said, as long as you don't get too caught up in the winning and losing of matches. Especially when you're beginning there is plenty to be learned in every situation in every match, the scoreline is not the only important thing, when starting out I wouldn't place much if any importance on the score and the most important thing is that it's a rewarding experience. When I'm playing matches I've got to try and find that balance of intensity and fun, it's not always easy but it's always time well spent
btw if you're pretty sure that you're going to take it up then I'd definitely recommend getting coaching (either 1on1 or in group sessions which are cheaper). Tennis can be expensive, having been at it for a year I have spent hundreds of euro.