Let's list what we can see in the photo:
- A common double triangle frame, but the top tube is duplicated. This was done for strength and durability. Sometimes this is called a "workman frame design" because early-to-mid 20th century, a frame like this could carry a workman to/from the factory with additional weight of tools.
- The front fork has some kind of suspension connecting the dropouts to the stem. This looks to be held on by a leather belt, and may not be working as intended
- Rod brakes - the brake levers are not cable operated, and the front brake isn't even there. The rear brake wire is visible under the downtube.
- Cottered cranks - these mostly vanished in the 1970s in the first world.
- A grease nipple or grease zerg underneath the bottom bracket, for greasing the bearings inside.
- The front fork tines have a large curve (rake) giving it a vintage look.
We can't really see the back of the bike, but it looks like a single speed, with no gearing. There has to be some kind of parcel rack back there to keep the load out of the rear wheel too.
The rear tyre looks positively recent compared with the front, there's a reflective sidewall, and the tread pattern looks quite different. Also the rear tyre looks wider than the front. The rear rim looks like the dull grey of aluminium, compared to the rusty look of the front rim which is likely steel. I think the entire rear wheel is off a newer bike.
Upshot its an old steel framed bike, dating from the 70s at the absolute latest. The rod brakes and zerg are features of pre-WW2 bikes. But its built like the proverbial brick outhouse, and has likely been ridden by multiple generations - I could see this kid's great-grandad riding that bike in 1930.
There are organisations and charities that collect bikes and repair, then transport the units to Africa for distribution. It's not impossible for this to be an Englishman's bike, which was donated, mechanically refurbished, and then shipped to Tanzania. For example: https://brightkidz.co.uk/initiatives/cycling/bikes-for-africa/
Additionally, Africa and India are two places where really old bike designs seem to still be made. While cottered cranks disappeared 40 years ago, it is possible that someone local is still making bikes and bike parts to those designs.
A google image search is unhelpful - this image has been used to illustrate many articles, and the texts don't generally relate to exactly this photo.
The wikipedia article gives a caption of "Tanzanian boy transporting fodder on his bicycle to feed his family cattle" You might try contacting the photographer via https://en.wikipedia.org/wiki/User:Muhammad_Mahdi_Karim and see what else he can tell you about his shot.
I found this list of bikes for sale in Tanzania, but none are particularly old: https://www.zoomtanzania.com/bicycles-cycling
For the purposes of your story, the brand and model don't matter at all.
- "Bruce rode the family bike - it was a hand-me-down from great grandad Bruce who rode it a hundred miles a day to work in the diamond mines"
- "Faded and rusting, with only fragments of the original colour left clinging tenuously to the rusty steel frame, fighting tenaciously to hold on"
- "Strapped together with an old leather belt, the old steel horse soldiered on over the years and decades; as babies became kids, kids learning to balance and ride, or learning to take a fall and get back on, and push through the pain of scrapes and grazes and blood. After all, the cattle need their fodder"
- "Bruce ignored the jeering of the rich kids on their fancy mountain bikes. He knew that ol'faithful wouldn't let him down. Maybe he's not the fastest nor the most comfortable rider, but at the end of the day this rolling squeaky rust-stained antique would get him home, and that sure beats walking."