Welcome and hello from me too. Naming rooms could depend on your surroundings or in the name of your preschool. My previous preschool was named after an animal, so the younger end was just the name of the baby of that animal. We just had two age block rooms.
Trees can be good as they’re gender neutral, ash, oak, beech, birch, elm, etc. you could even have seedlings and saplings for the younger end.
I can’t think of a life cycle that breaks down into so many discrete parts, so, as Sunnyday suggests, maybe you could just keep it simple and just use the age band names to avoid any confusion and explanation of what they mean.