The thing is: I do not think Gunn gives a **** about whether or not these actors can play the characters for 20 years, which is ultimately the actual concern you are talking about for being adverse at casting 40 something year olds, because does anyone actually doubt that Lee or any actor in their mid 40s for that matter could comfortably play Batman into their late 50s, an age in which plenty of action stars still do films with a lot of stuntwork? No. That is a complete non-issue. As long as they can do the 10 year plan, it's fine. I legitimately do not think that Gunn is even remotely expecting that whoever plays Batman in the DCU is still gonna be playing him in 15, 20 years. His main priority, as I think it is for every single character he's cast so far, is whether they fit the story they're telling now and that'll end in 10 years. There is nothing, and I do mean absolutely nothing in the way he's cast any of these characters, or any statement he's given, that indicates he's particularly losing sleep over the fact that any of these people might retire after 10 years. Hell, he most likely will be gone from DC after all this ends (he's gonna be 68 and I'd figure he wants to do other stuff as well) so why would he care if some of his actors retire with him?