Odds of Hanging On
Understand your market, build your brand, tune up your SEO (search engine optimization—a.k.a. how to be at the top of Google's results list), have a business plan, and you could build a pretty good business for yourself.
If you don't plan for success, you won't see any of it. You'll need to constantly be thinking about how you can make your business better, bigger, more desirable, and easier to find and buy from. Good customer service is a must, alongside some good business smarts, a steady stream of cool new products and designs, and a killer can-do attitude.
If you can do all that, then this job is yours as long as you want it. There's no age limit on how long you can craft; all you need to do is stay current enough to draw new customers in while remaining consistent enough to keep your old ones.
More importantly, you need the self-discipline and sheer stamina to be your own boss. That sounds great on paper, but it's actually a lot of work to set your own deadlines and schedule your own workday. Deciding what to do when takes up a lot of mental energy, and you'll have to have enough energy to design, make, and ship your products afterwards.
All this, combined with the fact that it can take years to turn a profit off an Etsy shop (and that it probably won't be a very big profit, unless you go viral), means that many Etsy sellers don't have lifelong careers on the site. You can only make felted bird ornaments for so long before you get kind of sick of them. Sure, they're nice, but you know what else is nice? A dental plan.