I think go for it. It will depend on what kind of thing you're proofreading but you'll mainly be spotting typos etc and the more you do the better you'll be.
As someone who regularly works with non native english speakers i find that however long they've lived here, and however fluent they are, they still tend to structure sentences differently and often miss out articles in sentences but that's not something that comes across in your original post.
Good luck.