The breath-alcohol reading is 4.5 x the permitted limit. I do not think the fact you are a new driver will particularly affect the length of the disqualification as the reading itself is the most influential factor here.
There is, however, a possibility that the court will attach an order for you to resit the extended test of competency after the expiry of the ban in light of the fact you have only been driving for a short period of time.
If you plead guilty at the outset of the case, the court should discount the disqualification (and fine) by up to 1/3. Consideration may also be given to referring you to the Drink Drive Rehabilitation Course which can also serve to reduce the ban by up to 25%.
I would suggest that starting point for the court will be in the region of two years and thereafter by applying the discounts, the net period of disqualification should be in the region of 18 months. I cannot see the disqualification being any less than 18 months in the circumstances.