Are there ways that healthy people can live together in group homes for mutual support and companionship?

Send, I like the idea of serving 6 months in a park. Is this through the National Parks Service? I did just check and see they hire Gardeners! Next I'll check the Michigan parks. Thanks for the great suggestion.

If you rent a senior apartment, they often have community rooms with activities, people who gather there just to wait on their mail to be delivered. Just stepping outside your apartment one can talk to others. Some have group transportation to grocery stores, movies, senior centers, etc.
These apartments are not necessarily assisted living or even officially independent living, but housing amenable to senior living and retirement.

One who is healthy can obtain a live-in position to care part-time for a child or another senior needing only companion care. Live-in, get paid.
Then, no longer lonely.

Another approximately 6 month living situation is for a senior to become a park host or camp host in a state park/national park. With summer arriving, you will get to live in a beautiful, remote environment, and not be lonely as you serve park guests on a part-time basis, selling firewood, admissions, etc.

It depends upon the definition of heathy senior or elderly.
Can you rent a large home and rent out rooms yourself?

Group homes are for the disabled and subsidized by Medicare/Medicaid.
What you describe is Independent Living and there are lots of them.