A small framed young child might be a good candidate to shoot a 243 but in my experience almost anyone who wants to hunt elk can manage a 270 or larger. I have a young woman hunting friend maybe 120 lbs who handled my lightweight 375 H&H just fine practicing for one of those TV hunting competitions,
My 12 year old grandson will be using his 30-06 for his first elk hunt this year he started using 110 grain minimum loads but handles 150 grain standard loads fine now.
We practice out to 700 yards or longer off sticks, knees or packs getting ready so that 300 yards feels like a chip shot. By the time we get to Colorado nobody feels the need to run to the sight-in days. Maybe if I were shooting a 243 instead of a 300 Weatherby or 7mm RM I'd need the reassurance.
I'm probably going to have 2 young first time elk hunters and a young guy on his 2nd trip in the group all of whom will shoot 30-06's with different Leupold scopes that will have way more rounds through them then they have today. The idea of handicapping them with a 243 or 6mm never entered mine or any of their thoughts - honestly I can't imagine thinking that way. But then again I like elk steaks and burgers and hate wounding animals.
