Re: when to do when....
So she's 4.5 months right now?
At this point, I don't think there's any harm in allowing her to taste solids. In fact, there's even some new evidence suggesting that early (i.e. prior to 6 months) introduction of solids may be protective against food allergies. However, I think the key word here is "taste." For a young baby, a taste is all that's required. So if you choose to offer solids, I'd keep it to a teaspoon or so.
Sometimes babies are interested not so much in food but in mimicking mama. So if you want to delay solids until 6 months, you could try offering your baby a spoon or a spoon and bowl to play with. That might satisfy her urge to experiment without necessitating actually having her eat anything.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"