im at 18 now, anyone having 20" arm could share some lessons?
Of course it is possible, but how anyone could help, if they don't know what and how you have training them at the first place? I can give you some rule of thumb's which I have followed and get closer to my own goals:
Less is more, and it gives better gains. WTF? 3-4 exercises, 12 sets, no more for that muscle group for 48 hours. Never think what is possible or not, just do it and look what happen. If you warm up your muscles, keep your body warm, use good techniques and full range of motion, you can't go wrong.
What I have done to get 19"(and growing) arms at the age of 60, is quite simple:
Warm-up = 20-30 reps with 20% of max set weight (biceps = barbell curls, triceps = cable push-downs). After this, start with the max set weight, which allows you to do at least 10 reps before failure. Next two sets same, but slightly less weights. I usually start with one hand concentration curls x 3 sets. After that barbell curls etc. but this time adding more weight per set, every set to failure, and end with Scott curls with same principle. For triceps same, start with the hardest set and max weight etc. and continue to other exercises. For me it would be machine dips(Hoist seated dip) with full range of motion, cable push-downs & and triceps push-downs with rope. Point is that in the first exercise your goal is start with the hardest load you have used, but do more reps than you did last time, and if you are capable to do more that 12 reps, add some weight for next time. Always full range of motion and good posture, no cheats etc. crap. You have to train so hard that you can't do these sets more than once a week, and you have to get at least 48 hours to pure recovery, so I do Chest + triceps + biceps on Monday, legs on Wednesday, and back + shoulders on Friday. Abs + lower back before every session. If you upper arms hurt like hell when you try to hold barbell to get decent squat on Wednesday, you have done it right
Problem with this is obvious: it seem to be too easy to be real, and that's why just about no one care to try. That is why they think it's can't be done, and cry about it in these forums..