We started try to teach some basic signs to DS when he was about a year old. He learned drink, eat, more and bath pretty quickly, but didn't learn anymore than those for a few months. Around 18 months old, he started showing a much bigger intrest in signing and picked up lots more signs. He knows light, quiet, book, please, thank you, moon, stars, bubbles, love, toothbrush, sleep, water and milk now too.
I don't think you are too late at all to start doing signs with your LO. I believe that it really helps them communicate needs and wants when they normally might not be able to. My LO seems to really enjoy it too, which helps.
We take our LO to see a developmental specialist once a year and she said that teaching signs to babies is great for them and does not hinder speech in anyway.
If your LO likes to be read to there are some great signing books on amazon.com that teach signs to children and my DS loves them! He has learned quite a few of his signs from those books. Here is a link to one of them: