They should be introduced on neutral territory first. Both dogs should be on leashes, and both should be told to sit, and when both are calm, let the older one go see/sniff the "new kid" and see how that goes. Watch body language, and if there's any sign of aggression, tug the leash to stop, separate them again, and start over. What kind of training has the "new kid" had, if any? Class would definitely help ...