For what it's worth, I (software engineer, 49) got a better job when I was 47. I got a job that I thought would be better at 46, too. But it turned out I was wrong, so I tried again.
My take, based only on my own experience, so grain of salt and all that: I think a business's status as a "startup," "enterprise," etc. makes a poor proxy for what it's like to work there. The correlation isn't zero, but there are a lot of factors. It's not simple. At any rate, it's really hard to know what working for a company will be like from the outside. It's good to have your shopping list of nice-to-haves, and it's good to ask lots of questions and try to suss a company out. But be flexible.
I've had the best experience finding work through former co-workers, people I'd like to work with again. There's a better chance of getting hired, you will have some inside knowledge of the company (good and bad) from the beginning, and you know there's at least one other person there who cares.
I'd recommend starting your job hunt immediately. Put out feelers with people you know. Look at job descriptions. Send out resumes. Work on any skills that need learning or refreshing. (But don't let perfect be the enemy of the good w/r/t skills.) Worst case: you're already having some conversations with potential employers when the axe falls. Best case: you've got a fresh job with a better salary before the axe falls -- maybe, by leaving, you even save someone else's job.
Good luck!