I am in a high rise condo apartment building (11 stories) that was built in the late 80s. My unit has the original piping. I moved there in June and I immediately realized that the shower pressure was reduced slightly when going from cold to hot water. The reduction was slight, and not enough for me to be concerned.
However, in the past couple of weeks the water reduction became more drastic, more than 50% reduction when going from cold to hot in the shower and the bathroom sink. There is one lever for control of hot/cold water in the shower. And right now the water is barely warm in the shower.
I also have reduced hot water pressure in the bathroom sink. There are two knobs for hot and cold at the sink so I am able to open just the hot and while the pressure is low, the water at least gets hot.
The kitchen sink is fine and cold water pressure everywhere is fine.