Your budgie is a sky blue greywing yellow face type II clearflight pied.
He is very young, looking at him I'd say he is 3 months old, he's clearly not gone through his first moult yet.
His cere will change colour at about 6 months old but this doesn't mean he will be ready to breed. Budgies are only fit to breed after they reach adulthood and this is after reaching 1 year of age.
It's never a good idea to place a nest box or any other type of nesting areas on a cage as that would only encourage breeding behaviour which will lead to unwanted egg laying.
In order to avoid complications and since you don't yet seem to have a good grasp of the species nor the required experience in budgie ownership, it's not at all advisable to allow your hen to lay a full clutch of eggs or to let her breed.
https://talkbudgies.com/budgie-breedi...s-new-old.html
Please remove the nest box, discard the egg and follow the recommendations on this link in order to break your hen's egg laying cycle:
https://talkbudgies.com/budgie-breedi...want-eggs.html