Look, the reality is that this specialty has a "shop" open 24/7/365. Now, if you owned a business that's open 24/7/365...How realistic do you think it would be to expect to never work nights, weekends and/or major holidays? Not very.
Sure, anything is possible and your best bet would be to land a gig with dedicated nocturnists, but don't count on it. Yes, if you pursue EM you're going to work nights. It's just in the cards. If you can't deal with that, then honestly....what specialty are you going to pick? That cuts out surgery, IM (hospitalist), EM, Anesthesia, Ortho, etc.. You do realize all these specialties work nights when they are on call, right? You'll be fine. You get used to it.
To more specifically answer your concerns about having to work nights later in your career... Yes, you're going to still have to work them. Especially if you work for a CMG. The beauty (or curse?) of a CMG is that everyone is on an equal playing field insomuch as compensation, hours, schedule, etc.. So, you get to hit the ground running as a new hire and are making just as much as Dr. Moses who's in his late 60s. Then again, when YOU are in your late 60s, you'll be expected to "pull your weight" and that includes working your share of nights, weekends and holidays. I'm always extremely fair with all of our docs when making the schedule and I run a statistical report every few months and adjust nights accordingly to make sure everyone has the same percentage. Ironically, the only ones who complain are the younger ones.
You might have better luck as a senior partner in a SDG where you can cash in on seniority perks but I wouldn't count on them still being around for too much longer. Alternately, I suppose you could find a CMG that was really desperate for a new FTE and negotiate limited or no nights into your contract, but I wouldn't recommend it as the rest of your colleagues are bound to find out and that won't exactly make you the popular kid on campus. We had one guy like that who insisted on no nights after he had a heart attack and was given a pass for "health reasons". It used to give me such an attitude because he smoked like a chimney and I would have to give his nights to everyone else including one of our docs who was early 70s and has since retired (thank God...That's what 4 divorces will do to you!)