By "have a job," do you mean he needs to earn money, or that he needs a regular and structured activity? I hope you don't mean he needs to get paid - that's a lot of stress on a child if you have him in a typical employment situation, and there are tremendous restrictions about how much a company or enterprise can pay (child labor laws, etc.). And I'd have some concerns about a child that age around a tractor or other piece of heavy equipment - the liability for the farmer is huge.
And I read your added information, which somehow got posted as a regular response below, instead of being added to your original question or posted as a "So What Happened" - can you copy/paste that into the body of the original question so everyone sees it?
Since he's an introvert and doesn't enjoy camp, but he does enjoy animals at least a little, can you consider the following? Maybe some of them could be done with his younger brother.
- volunteering at an animal shelter or rescue operation for abandoned animals. They would LOVE to have someone walk, feed, pet the dogs and cats. Sometimes they need some small repairs on crates and pens which might appeal to his hands-on skills, or he could work with one adult volunteer to learn how to do more things.
- providing foster care in your home for an animal that is over-stressed in a shelter (maybe do this after he does the first one, so he gets some experience and supervision from the adults. Some of these abandoned pets don't do any better in the noisy and crowded environment of a shelter than your son does in the noisy and crowded environment of a camp. I wonder if he would have some empathy with them.
- providing vacation coverage for neighboring families. When they are away for a day or a week, they might need dog walking or cat care (not just feeding but also socialization for lonely animals - which takes more than an hour a day). For more than day trips, they might also need garden weeding/watering, mail/package collection, houseplant watering, and so on. My son started this at about age 10, adding responsibilities as he got older, and had quite a business going by high school! Money, responsibility, flexible schedule, very part time hors. He also learned to write up invoices on the computer and keep some very basic financial records, and he opened a bank account. Great prep for "real life."
- volunteer at small-scale summer programs, like track clinics or town recreation programs for younger kids, if he's in a smaller group with younger kids that might be less stressful than a bunch of his peers.
- volunteer at a nursing home or assisted living residence to help with activities. Seniors often need help with things like crossword puzzles, bingo games, or craft activities. Sometimes reliable family pets or foster animals can be taken in for engagement with the seniors - good for everyone. Some residents may have bird feeders outside their windows which need to be refilled or cleaned out - it gives them so much pleasure and it might be emotionally rewarding for your son.
- Do an area collection for needed materials by the food pantry or the animal shelter. We've collected old bedding/towels/pillows/bath mats as well as donations of food and bowls (etc.) for the shelter. Your son could make up flyers, explaining what's needed (after he talks to the agencies), and distribute them to neighbors or post at the library and other public bulletin boards. He could, perhaps, set up collection bins at a pet store (for animals) or the supermarket/library/police station (for the food pantry). He could go in once a week and collect donations and take them to the recipient agency. Maybe he could set up something at an area farm stand to collect extra produce or get customers to donate part of their purchase to the hungry. That would give him a start with a local farm and perhaps show enough dependability and interest that would lead to a job in future years.