At two years old, my younger son was finally able to keep his center fingers down to sign "I Love You." Until that time, he signed it with an open 5 hand. Both of my children demonstrated understanding my signs around 4 - 5 months. They began to use signs at 6 1/2 months, and put two signs together around 9 - 10 months.
Remember something very important--- they saw me signing since the moment they were born. I already knew ASL... I didn't have to learn a new language and way of communicating at the same time I was learning to be a new mommy.
So relax. Give yourself time to become comfortable signing. Enjoy the process. Give your baby time to take it all in--- and once you think he/she understands you, give him/her the opportunity to express needs & desires.
We have had children in Baby Fingers classes begin to sign at 8 months, and others not until 18 months. There have also been children who never signed but began speaking-- really clearly speaking-- at 15 months. Their parents directly credit the exposure to sign and the focus on language in general.
As Etel said so elequently below, there are benefits at every age and stage of development. So expose your child to language from day one, and to signs as early as you are able... that could be at 3 months or at 2 years. And again, enjoy the process... you will enjoy the results!
To read my Mother's Journal of my children's sign development, take a look at the OUR STORY page on www.mybabyfingers.com. Happy signing! :) Lora