welcome to ology bro. unfortunately you are not ready for any steroid. no offense but you're body weight is significantly below average for your height, let alone for steroids. Steroids at this age will also hurt your natural test production and prety much guarantee to stunt your growth whether it be your height, shoulder width or any bone growth. nor am i convinced that you have a few years of weight training under your belt. if you had you'd weigh more and you wouldn't be asking to get cut up at 140lbs, because you would have been shredded had you been training. with all 3 issues combined steroids will only hurt you.
we would recommend you eat like an animal and train for the next few years. start collecting creatine and nitric oxide supps for your journey, make sure your protein intake is high. for your body weight i recommend you aim high on your calories, eating 6-7 times a day, and up your carbs as well.
start becoming familiar in the training section and the diet section of this forum.
good luck, i hope not to see u posting on the aas section until you've hit at least 180lbs and 25yrs of age.