It depends on the 70 year old opponent. I know 75 year olds that can still hit a great forehand, so I tend to hit to their backhands. On the other side of the coin, I occasionally play doubles with older folks who don't move very well and I don't drop shot them, out of respect. But normally I don't play with folks that old, because it's too one-sided so not a good matchup for anyone. I happen to be 49.