You have a lovely sofa there Hosman. Most importantly you both like it and it's comfy!
I'm no expert on casters, but they look quite old from your photo. I've been crawling around the house on my knees looking at ours. We have a late Victorian/early Edwardian barley-twist cottage suite, they have pierced casters, but condition looks the same as your photo. We also have a Victorian Iron & Brass bed, solid casters, again very similar to yours (a good job that I did look as I just noticed that one was damaged!).
It looks in lovely condition, and I'd say that it's certainly no later than 20s - 30s ... but others may have a more informed opinion.
Nice find!