John Muir guided hike

You might try Sierra Mountain Guides.

Holly –
I hope this does not offend you, but WHY a guided JMT hike ?
I've always urged people to take the trail of self discovery, meaning do on your own terms at the limit of what you are capable of at the time. As your skills improve this trail of self discovery can lead to more and more challenging outings, but always on your own terms.
To me, this trail is much more fulfilling than being guided along like a sheep.
Whether clmbing Mt Everest, or El Capitan, or hiking any route, allowing a guide to provide the comfort/safety net only deprives you of the feeling of maximum fulfillment that doing something on your own gives.

I'm not saying don't use others to gain skills, but use the skills gained to accomplish your own goals on your own terms.

Holly, a lot would depend on what you are trying to do, and the "whys" of wanting a guided trip. By "younger average group range" do you mean kids? If you are asking the question at all I suspect you are less interested in the voyage of discovery that art is referring to than maybe a one-off – is that correct? The eastern Sierra in particular has a lot of *outfitters* have guided and semi-guided (providing easy initial access for gear and food) trips due to the easier access on that side of the mountains, but I mostly have heard about horse packing. You can call the usual suspects – there are 4 or 5 down the stretch of the eastern sierra from hy 20 to lone pine, each that cover approximately the areas near them, that you might call, and see if they offer something not involving horses.

http://www.owensvalleyhistory.com/pack_stations/page54.html

I suppose the "problem" is – what do you imagine the guide will be doing? If you want them to provide everything that is one thing. If you want to bring your own stuff and walk yourself, that is another. I think you might have a bit harder time finding something for the latter – what would they do, and how could they charge you enough to make it worth it? If the former, and you are starting from scratch with an inexperienced group of people, maybe consider horse packing in and out with one of these companies, and spending several days doing day hikes for bases camp. Might be as good an intro as you could get to some really remote and/or high up locations quickly and then get a taste.