You may want to try separating them. The best way is to put the new kitty in a closed room where the door has a little space underneath. That way they can smell each other and stick their paws out for each other. This may take a week. During this time if you notice a little interaction take them out to have some supervised time together. Since one cat is significantly older he probably just can't stand the activity level of the younger one yet so when you do your supervised introductions try to find a time when the younger one is a little calmer. Most cats are calmer mid morning and very active at night. Mine prefer 2am - 5am to wreak havoc. Cats are colony members so it may take some time to re-establish a hierarchy, yes even with just two cats. They may never completely like each other but as long as they aren't causing extreme harm to one another they should be okay.