When I got Hallie she was 2.5 and had never been socialized. She was so very shy and timid around ALL other people and other animals. The vet suggested I start taking her to daycare with Simon (which I did and still do) and also to take her by herself to special places. I started walking her alone and taking her to Petsmart and that seemed to help. My trainer also has me take her to an outside mall just to walk around and interact with other people. The best advice he gave me was to take Simon and Hallie separately so they can learn without distraction from the other.
I don't think it's ever to late
Good Luck