In fact I started giving my dear son beetroot puree when he was only 5 months and he took to it very well. I used to combine it with carrots or apples. NAturally beets have a sweet taste but they dont't mash very well so you could add beetroot puree to your baby's porridge or give it to him on its own as a snack inbetween meals.
But BEWARE that when you baby eats beets, the stools will have a red tint to it. dont be shocked, it's definitely not blood he's just passing the beetroot out.