No more spinach.

I didn't agree with you on the GT MTB idea since those are becoming cult status, but I love this idea. :) There are 26" and 29" versions of Monocogs

Ah, you're in PDX? That (as you probably know) increases your price point, but you also have a few co-ops down there that might still have some frames available.

if he insists on fixie (have a son like that) consider gettng a quality frame either used vintage and if need be use a singulator for chain wrap, or someting like the soma rush https://www.somafab.com/archives/product/rush or a surly steam roller https://surlybikes.com/bikes/steamroller

another option (knowing kids, even big adult ones) is a vintage geared bike that will take fenders and find a gear he likes and then tell him not to bother shifting :)

Maybe find something that is tough, but will also have great ride quality. Basically, anything in Columbus Aelle, Chromor (Matrix), Thron, SP, SPX...

Oh man I forgot about those. If you can find one that would be an awesome bike.

Fixed gear with a chain tensioner is a no-go.

Fenders with track ends can be a PITA, so if you go that route I would suggest a full-coverage front and something like a PDW clamp-on rear fender.

I'd probably go with a good quality vintage roadie and run it fixed. It should have all the right provisions for brakes, fender mounts, and forward facing angled dropouts that make taking the rear wheel out with fenders a non-issue and allow you to get proper chain tension without a tensioner.

State bikes also make a pretty good fixed too. 4130 double butted fully built bike for $460.

A Langster might work from around 2010
[url=https://flic.kr/p/CquLb9][imhttps://live.staticflickr.com/5641/2...765db483_c.jpg2010 Langster Steel 61cm, on Flick

No light weight at 22lbs as shown.

^^^^^ 32-spokers might not be apropos.

So Young Spadoni drops by today. I tell him what sage advice the denizens of BF offered on his next bike and showed him a couple bikes on CL that he could consider when he was ready to buy a new steed. He left, and I expected to hear nothing for months. The lad likes to ponder before acting. But not this time. A few hours later, he texts me to say he has bought a Cannondale! With multiple speeds! And functional brakes! I am still awaiting photos, from the drive side, of course, to further I D said bike, but as Squirtdad suggested, kids will surprise you. This one sure did.

If if they were so bad, why are there so many of them still around? Especially the XXLs; I can’t swing a dead cat at my CL without hitting a 62cm 3.0 or R800.

I'm 6ft 3in tall, and in my younger days, when I was far more fit, I was around 280 lbs, now I'm closer to 400 and I lost an inch or so of height. Back then I used to break frames, break cranks, and wipe out freewheels all the time. The frames were usually broken either where the downtube meets the bottom bracket or across the chainstays just behind the BB.
One broke mid headtube but it broke early on in the frame's life so I more attested that one to be a defect.
Cranks were the hardest to take as they usually hurt when they broke, the frames would give me a warning and usually get me home unless it completely separated at the stays. I had one later Raleigh separate its rear stays at the seat tube.
I didn't ride fixed gear though, I'm not sure how that comes into play with frame strength but I could see it being hard on cranks.

Hardening Aluminium to be avoided by the gorilla.
 

If you have a breaking frame problem, stay away from Al bikes - especially second hand . Al work-hardens and it will crack if you exceed its yield strength and will simply crack with no warning.

This is why no one uses Al rims anymore.

Or handlebars.

Or seat posts.

Or steering stems.

Single speed from fix gear is a BIG step down if he has fallen in love with riding fixed. If I had to make that choice I'd stick to gears despite fix gears being my number one the past 40 years.

I'd look at exactly where and why the frames are breaking. Shouldn't be happening; at least not until a few years of hard riding have happened Too short a seattube (that saves the work of mitering the tube to fit the other tubes)? Faulty BB shell?

Possible solutions for your son - an older style track bike. Those bikes are built to handle strong 200 pound riders in competition. (Well not all but the bikes used in Velodrome fleets, yes. The Fuji track bikes of not that many years ago have been used as fleet bikes by many velodromes. I've seen very big and strong national riders show up at our local Alpenrose track and rent Fujis rather than fly with their bikes.) If there's a track nearby, call them and ask about such bikes.

I had a co-worker who went through Miyata after Miyata in the early '90s. Always broke at the brake cable exit on the top tube. Miyata always honored the warranty but he spent real time without his transportation for a 20 mile each way commute. I've heard since that many of those early internally cabled Miyatas broke, Yes, he was big and strong, but like your son - still ...

Edit: MIssed the second page. Oops.

Ben