I think taking an AI at your age is a good idea but I wouldn't recommend Novedex XT.
Why do I think using an AI at your age is a good idea?
(1) Your epiphyses may not have yet closed and using an aromatase inhibitor may enable you to gain more vertical height. It was once thought that closure of the epiphyses was governed by androgens but it is actually governed by estrogen
[1][2][3] By using an aromatase inhibitor -- assuming your epiphyses haven't closed -- you will be able to delay closure of the epiphyses which will enable you to grow taller
[4][5].
(2) Using an AI will boost your androgen levels in a way that will not disrupt your HPTA or damage your liver. This will help you get the muscle mass you want.
The epiphyses close at around age 20 in most people so you may have a chance of growing a little taller.
I suggest you try Exemestane at around 12mg/day.
Using an aromatisable AAS or even a testosterone booster (other than an AI) without an AI if you are under 20 could prevent you from reaching your genetic height. Your 18 year old friend could be prematurely terminating his vertical growth period. Androtest isn't an AI, its a forumulation based on the herbs Tribulis Terrestris and Eurycoma Longifolia (I don't know about the efficacy of these herbs in elevating testosterone levels). An AI is an aromatase inhibitor i.e. a substance that inhibits an enzyme called aromatase which catalyses the conversion of testosterone to estrogen. Neither Tribulis nor Tongat Ali act as AIs. AIs act as testosterone boosters but not all testosterone boosters are AIs. Is this distinction clear in your head?