Just saw your question. I'm 73 1/2 and still lifting hard. I have to make some concessions to age but I can live with them. Living in a huge retirement community near Orlando, our nearby gym doesn't have a power rack so I have to use a Smith Machine for Squats and Rack Deads. I also use it for my BP and Close Grip BPs because of a problem with tremors in my right hand. I can still use a decline bench however. I rotate months of low weight/high rep/short rest with high weight/low rep(1-5)/longer rest for my training.
If you are still at your 50 year old level you are doing fantastic. Not many guys lift seriously into their 50's and very, very few into their 70's. Most simply lose the drive and commitment needed to stay so strong, much less continue to grow. I find doing my 3 X 5s or sometimes 5 X 5s and alternating the next week with 5's for warm-up and singles up to my max to be a way to still sneak in increases of say 5 lbs. on the big lifts. A key element in my strength and growth is rest. I need longer now to recover between sets and between splits so I/we (my Dutchess is in fantastic shape for 70 something herself) lift on an 8 day week with 4 splits spaced every other day. Hence we get a full week to recover from heavy workouts. We need it LOL. This past week eg. I singled at 310 on the BP and yesterday did 5 reps @ 370 and 3 @ 420 in my Rack Deads after just 2 months of being back into training heavy. My goal and IMO an achievable one, is to hit 330 in the BP and 530 in RDs within 6 months. I simply can't push faster than that or I would risk almost certain injury. Those are my concessions to age, but they are livable because I can still have that great physically strong feeling and catch a lot of attention at the pool etc. Just more motivation.
We eat a pretty clean diet but IMO it is our supplement regime that allows us to keep training and even growing despite our ages. For example I take megadoses of vitamins such as