I'm 44 and I train no gi more. I enjoy takedowns, which are less of a thing in the gi. Gi grips tend to hurt my fingers. I only weight around 135 and I find it much easier to deal with larger opponents in no gi. In the gi I find it is easier for them to latch on and use their strength and size.
No gi has more movement and a faster pace, but I wouldn't characterize it as speed and scrambles. The most speed and scrambling happens with white belt wrestlers and it decreases from that point on. These days I don't roll with white belt wrestlers very often.
As for leg attacks, I don't feel that they are harder on the body as long as you are emphasizing control over positions rather than quickly trying to catch a sub or trying to escape explosively. Doing it that way will result in injury no matter how old you are.