They are all made for a global audience of casual viewers who don't care who plays Han Solo anymore than they cared who played James T. Kirk.
If this is really true, then it cuts both ways, and directly undermines your statements about Carrie Fisher. Self-contradiction - good luck with that.
Because it's Hollywood, babe! it's a cruel biz.
Tell that to Dame Judi Dench, Helen Mirren, and a host of other actresses, or Christopher Lee for a male counterpart. Star Wars doesn't seem to be a franchise that has considered age and attractiveness to be a large factor.
What I see for Episode 7 isn't a young/old, either/or situation. Rather, what I envision is a both/and, in which the older cast and a younger are blended for a single film and the cast looks a bit more like the recent Dallas reboot on TNT.