Starting C25K at age 42, heavy with a bad ankle? Am I nuts?

I'm not an expert of any sort, so take my experience for whatever it is worth... I broke my ankle and had it surgically repaired with a plate and it is now pretty arthritic. I broke my ankle in 2002 and I am now 49 yo. I started running a few years ago with the goal of just a 5K. I never consulted an ortho on it, but my regular doctor never had an objection to my taking up running as long as I listened to my body and didn't push too hard too fast. I still have weight to lose, but am currently significantly (about 40 pounds) lighter than when I first started running. I have stayed with it and in January this year I completed my first half marathon with more 5Ks, 10Ks and half marathons on the calendar for the next year and a half.

You could give it a try and see how it goes, take it slow and be sure you are running in good shoes - go to a running store, get your gait analyzed and pay attention to your ankle and listen to what it is telling you.

Plenty of people start running after 40 and overweight and are fine, just give it a try and see how it goes. Main thing is to ramp up slowly, which C25K is perfect for. Don't run more than it says in the first couple of weeks, even though it might seem too easy.

Make sure to ice and massage anything that gets sore. If your bad ankle gives you trouble, go to a dedicated running store and let them advise you if you need stability/support shoes.

My wife has arthritis in her knees and ankles and never thought she could run. A couple of years ago she got some custom orthotics made. They're expensive but allow her to run pain free.

I would trust the physical therapist. As someone who also has post-traumatic arthritis and loves running, I would not risk it. At least not until losing weight. Walk.
And since it is arthritis, shoes will not fix the problem. You risk ending up unable to walk.

I started C25K in August 2014 weighing 230lbs and having never run AT ALL before then. I was 44 at the time. For extra benefit, I also had my ACL replaced in 2008 at which time the ortho told me I had some arthritis in my knee.

Now, a year and half later, I'm down to 160 and finished my first half marathon at the beginning of March.

It IS possible, but as the old saying goes, "Slow and steady wins the race." The biggest cause of injuries in runners is doing too much too fast. Follow the program and repeat weeks if you don't feel ready to progress. Just don't quit and you can get there.

All of this comes, of course, with the caveat to trust your doctor/PT over some rando on the internet

Agree with everyone else, slow and steady.

Also Hoka One One's might not provide enough support for someone at your weight in regards to running. It is a lot more high impact than walking, and I think the Hoka One One's are meant to be a bit minimalist, which can be risky for heavier people running.

I think if you start run/walk 3x a week, with a mandatory rest day inbetween, and take it easy and slow, and if you get injured take time off and just repeat the week rather than push yourself to keep going. I think the only special advice I will offer is, beware that your cardiovascular fitness might outstrip your muscular fitness in the beginning. So really hold yourself back even if you "feel great" and want to go faster or go longer. After a couple months your body should adapt and you can push yourself more cardiovascular-wise.

I say give it a go, the risks seem low. Maybe have a backup plan for exercise if something prevents you from running OR walking. Like could you cycle or swim? If you have that in your back pocket I think you'll be fine.

Im 44 and started 4 weeks ago. It surely isn't as easy as it would have been 20 years ago, or even 10 - but it isn't supposed to be easy! Go for it. Take it slow and listen to your body. Treadmills are easier on the joints than concrete. Rest every other day, or swim, or do something different. And invest in good shoes and good socks. Don't try to RUN, just trot, or jog until you're ready to pick up speed! (Telling myself all of the same things).