At 70 years old.. United you get serious with lessons and a going to range. Your swing will not change that much.. however there are minor fixed you can do. I am a certified fitter at golf galaxy and I fix this.. at least for the fitting and if they listen longer without much work..
There are two things you can do that could fix this with your driver.. 1. Put the ball more forward in your stance I’d say 3 balls more forward in your stance then adjust from there. Putting the ball more forward in your stance will allow the club face more time to square up.. although it is probably fractions of a second it can make all the difference..
2. Strengthen your grip.. so for a right handed golfer.. rotate your grip to the right.. putting your left hand more on top of the the club and your right hand more on the side…. Doing this will naturally help you close your club face quicker..
Both of these things by themselves or in combination with each other can help you fix your slice without having to change your swing that had been ingrained in your for 70 years. Try it out let me know how it works