I've been reading some of the reaction to the 'casting' of the big three in mainstream media and in some forums and I have to say I'm shocked at how agist some of it is. There's this idea that the three OT stars are too old to 1) carry the movie and/or 2) be any good. I think it's ignorant. I don't believe they will be the main focus of the ST but let's say they were - all three of them have proven in their own way over the last 30 years to be too talented to be treated this way. I doubt any of them will be running around with blasters like back in the day, but you know, SW over the last 15 years hasn't been so good that it's too good for these guys.
If your thing is you don't want to see them because for you they're frozen in time - you don't want them to come back and die, you don't want to spoil your memory of them - I get that. To me that's separate.
I do think there will be a younger generation of heroes. The more I think about it, the more I'm certain (and therefore will be wrong) that the protagonist will be a Solo. Whether he's a he or a she, they're going to be a rogue like dear old dad and will have rejected their legacy (think Cade Skywalker) because it's you know, filled with genocide. As one of Leia's children, they will probably inherit her POV on Vader, which is not as informed as Luke's. Vader stood there and watched as the Empire destroyed her planet. Luke may have saved him, but he may be beyond redemption for her - and as someone who grew up separated from her true legacy, Leia may be intentionally or unintentionally walling off her kids from their past. What conflict this would be with Luke - I'd pay to see it.
It will be the Solo kid's test and Luke's to realize their destiny and do the final accounting on all this Jedi/Sith business.