How to cope with an aging cat?

hello everyone, my cat is showing some clear signs of aging, and it has me in tears. she has been with me for four years, found as an adult stray. I have no idea how old she is or how much time she has left, which kills me. She’s the absolute love of my life, and I’ve never been solely responsible for a pet before her. How do I handle the emotions of knowing she won’t be here forever? I’ve just been silently sobbing at my desk at work for the past 30 minutes.

I’ve included some pictures of her for reference and enjoyment. It’s hard to get pics with her eyes open because she’s always smiling at me (and/or sleeping).