Along those lines, the up-side of learning tennis when you're young is that your game can peak as your body peaks. You can really reach your full potential. The down-side is that you spend a looooong time thinking about how good you USED to be, as your body declines.
On the other hand, those that take up tennis as an adult (after kids are mostly grown or maybe even out of the house) can improve for a long time. At nearly 52 I'm now a better tennis player than I was at 30. Even though I'm not as fast or strong as I was a few decades ago, I can still see my game improving. I'm hoping it will continue to improve for a few more years before everything starts catching up with me. With any luck, by the time my game starts going downhill, I'll be about ready to kick the bucket anyway.