The Astral dress is a made to measure and size inclusive design, this means you take your measurements as indicated in the pattern and then follow the pattern instructions. This means it can be made for any size and age.
The pattern is an advanced beginner level and uses US terminology.
You will need any type of 6ply (sport) weight cotton yarn and a 3.5mm crochet hook, you can use a 8ply worsted weight yarn if you prefer but I suggest you go up a hook size and please note your gauge may be different.
For the sample size (UK 8), I used roughly 1200m of yarn.