Mid-career shift to law practice?

I find myself mid-career wondering what it would have been like to practice in a law firm setting. I’ve been in academia (non-faculty) since bar passage, doing research and advocacy on legal issues. I’m pretty entrenched at this point, in some super niche legal topics. Would it even be possible for me to join a firm? Has anyone made a transition like this? Do firms even hire old bags like me when so many fresh students / new lawyers hit the market every year? TIA for your thoughts and experiences!