There are many variables that contribute to your baby’s signing “start-time.” Meaning, that not all babies start at predictable times. This is due to:
The age of your baby. An older baby will sign back faster than a younger baby, generally.
Your baby’s ability to coordinate their body. If your baby is pre-occupied with another development milestone like crawling or walking, signing may be delayed. Baby’s under 9 months of age are still learning to control their little body’s and might need some extra time to work this out.
Your baby’s temperament and interest. Maybe you have an introverted baby or one who’s more interested in playing than socializing. Perhaps you are teaching signs for things that don’t amuse or fascinate them.
Your level of commitment. The more you work at it and expose them to signs, the faster they will pick it up.
Your level of consistency. If you sign in fits and starts, so will your baby. The more often you do it, and how regular you are, the quicker your baby will sign back.
How much help you have. Let’s face it, having an army of signers around your baby is going to speed things up. If your baby has siblings, grandparents and family friends signing up a storm around your baby, they are bound to sign back in a hurry.
Obviously, some of the above conditions are under your control, and some aren’t. If you really want to succeed then make up for what you can’t change by adding to things you can. If you don’t get early results, then just try again later when your baby is a little bit older and more coordinated. Try to get your baby when they are relaxed and calm instead of focused on something else. Boost your consistency if you find yourself inconsistent, and if you can involve other people that are part of your baby’s life, then do so.