By Darren Franich
September 25, 2017 at 02:00 PM EDT

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Jim Parsons just started working on season 11 of The Big Bang Theory, and the Emmy-winning actor sounds energized. “We laughed our asses off at the table read,” he says, describing what happened when the cast sat down with the script for the Big Bang premiere. That episode promises to pick up where the cliffhanging finale left off, with Parsons’ Sheldon down on one knee asking longtime girlfriend Amy (Mayim Bialik) to marry him.

Did the engagement come as a surprise for Parsons? “If you’d have told me nine years ago, I’d have been like: ‘Oh, well, that must be when we need ratings help,’ you know what I mean?” he says. “‘I guess we’ll adopt a monkey next.’ And instead, it makes all the sense in the world! It feels like they built towards it.” And what happens between Amy and Sheldon after that proposal? “So far, no one’s been left at an altar yet,” he promises.

Sonja Flemming/CBS

While Sheldon enters a new stage of his life, another era will also be explored separately, on the origin series Young Sheldon, co-created by Big Bang executive producers Chuck Lorre and Steven Molaro. (Parsons narrates the spin-off and is an executive producer.) With Big Bang entering its second decade, how much longer does Parsons imagine playing the character? “I don’t think you’re gonna see a geriatric Sheldon,” he says. “If you do, they’re gonna have to cast it quickly, and with somebody else. Old Sheldon, coming next fall! Oh, Jesus, I think I literally just heard Steve roll his eyes somewhere and Chuck groan.”

Big Bang isn’t ending anytime soon, of course. “We have this contract now that goes through season 12,” he notes. “Who knows what the future holds, but let’s say it ends in two more years. Let’s say that’s it. There’s no way, as an actor, I’m going to feel anything other than: ‘We left that all on the table.’ It’s been a wonderful ride. I’m fulfilled in so many ways.”

And if the show should end after season 12, Parsons views successor series Young Sheldon as a helpful bridge — and not just for the viewers. “Knock on wood, if [Young Sheldon] goes on for a little while, I hope it has a somewhat incidental therapeutic effect,” he explains. “Certainly on me, maybe on the cast as a whole. It may help the death not be quite as total.”