15 month old DS loves tea. He's had a sip of mine a few times, and will polish off dregs of any mugs left sitting around, if you don't watch him closely.
My DM made him a beaker of very weak, milky (about 50% milk) tea, no sugar, at her house the other day, and he loved it. It's not something I've ever done, but just wondered at what age most people think this is ok. I didn't drink tea until my teens.