You can, but I think it will be a lot of work. Are the tags silver or orange? The vaccination tags would be orange, but look close, b/c if the tags are old, the color wears off. The inside of the ear should be the right color.
For a quick and easy test of "old or young" pinch a piece of skin on the cheek and pull it out an inch. Let go. If it quickly returns to its place, it is a young cow. The longer it takes to return to spot, the older the cow.
The best method is to look at the teeth, but I don't know the aging rules on that. It doesn't matter to me how old a cow is as long as she is producing a calf every year and moves well. One that lays down a lot because of arthritis should go to the sale barn.