When trying to improve your writing, should you ignore 'old' books or embrace them?
The answer depends on what you intend to do afterwards. If you're reading a Thomas Hardy books do you intend to write in that style? Hmmmmm.
If, on the other hand, you're just enjoying it for its own sake, no problem.
There are, however, things we can learn from old stories and books. I'm slowly working my way through a collection of short stories by Ambrose Bierce. I've noticed that he often starts with a description of the area in which the story is set. It's not a description of every tree or the colours of the leaves, but a description of the impression the area makes on the character.
I decide to try that approach with my novel and found that it worked quite well.
How old should you read? As old as you want. Good writing is good writing, no matter when it was published.