You need to wait about 6 months for your tank to become established, and for you to become experienced before adding an anemone.
A 29 is a bit small, it can be done. I don't recommend it unless you have experience with anemones. Your water quality can go down hill pretty fast in smaller tanks. You also won't have room for much of anything else when the anemone grows. If you plan to keep corals, the anemone will sting them.