Also slightly too old for a role that might run at least a decade unless you are aging up the rest of the Fantastic Four (which you could do by starting midway through their career).
Yes, please. No more origin stories -- the FF's origin is the least interesting thing about them, and even their debut comic reserved it for a relatively brief mid-issue flashback. What's interesting about them is their role as an established hero team and family, prominent and respected within the Marvel Universe. They could've established themselves during the Blip years, with Reed moving into the void left when Tony Stark withdrew to his cabin.