Is it me, or my gear?

I have a 70-300 mm Olympus Zuiko lens that is my go-to for most photography. I've had this lens since 2016, and it's my second 70-300. Lately it seems to have trouble focusing at it's farthest range, like when I'm trying to photograph birds at the feeder. The auto focus struggles to find the subject, even when it's fairly large. I'm terrible with manual focus, so I rely on auto especially when shooting wildlife. Do you think these lenses (I'm talking lower level DSLR gear) have an expected life span? I do keep the connections clean. It's very frustrating when I look at the quality of photos over the last few years and see them getting less and less sharp, but that could be because I used to shoot daily for years, then stopped completely for a while. Maybe I just need more practice?

My gut feeling is it's probably the lens. I had similar with my 18-200mm last year and had to replace it.

Way back when, I had a bridge camera (Finepix HS10) with a fixed lens, which on the face of it sounded good for where I was. Then it started to have problems focussing so I took it to a repair shop. He explained that each time you zoom, you wear the lens when then becomes loose. The life you get out of it depends on how much you zoom, and I had basically worn it away. With a bridge you have to bin the camera.

So my guess is that could be the problem and it's sadly new lens time. If it's any consolation, that's probably cheaper than my problem which is the body.

I'd love to upgrade all around, but I have so much money invested, it's difficult to let go.  Especially when you know the gear is older and will only trade in for a fraction of what you paid for it.  This is my second Olympus (E-620) and I purchased it used many years ago.  It's not a terrible camera, just old...like me.  
I appreciate your input on the lens. I think maybe I can live with it for another year and decide if I want to upgrade or keep going with what I have.

Have you looked at 2nd hand? I use MPB, they have a wide range at reasonable prices and it's all checked. Plus when I had a problem they honoured their guarantee without a quibble. You've probably got other 2nd hand outlets, too.

I'd second that. There are some great bargains to be had in the second-hand market, especially after people have traded up for mirrorless bodies and their dedicated lenses.