Is it ever to late to socialize your dog?

My dog just turned 3 this past march, and she is still very anxious and barks at people she meets. when i take her for walks her hairs automatically stand up at the sight of even the farthest person. I know that this is hugely my fault for keeping her in the house all the time and seldom walking her, but I'm walking her much more often now, and she still seems to react the same way. Id really like for her to be more comfortable with other people and other dogs can any one give any suggestions.