Great advice by many above. Let me say great progress you have made thus far -good job young man! Now, your answer lies in your pic. You are very vascular, which also goes hand in hand with being very lean. THERE is your answer my man. While being very lean is great to step on a stage and compete, it is NOT your friend when trying to grow - ESPECIALLY at your age. You with me so far? Your answer, your magic pill, yoiur Holy Grail issssssssssssssss...................................FOOD FOOD FOOD! Considering how lean you are, FOOD will do more for you than steroids at this point. At your age, you are ALREADY on a "natural cycle" amigo - your testosterone levels are as high as they ever will be, and will be for several more years.
Now your prolly gonna say like most young guys that hit me up at the gym frequently for advice on how to get big - "But I AM eating. I eat all the time. I take in 5k cals a day and STILL can't grow." Two points here:
1 - They say they are taking in 5k cals. That's BS 99% of the time. They are just trying to quickly cover their azz by saying that, hoping to get that out of the way so I can tell them some "magic secret" to getting big. How do I know this? Bcoz I tell them to get back to me in 1 week - I want them to write down everything they eat & drink, every day, for 7 days. When they get back to me, I tally everything up, I then SHOW THEM the results. That 5K cals turns out to be more like 2800 cals duhhh! Ya see, most young guys are impatient and just eat, and while they may be eating the right foods, they damn sure don't have time to actually calculate literally everything they are consuming over the course of a day, day in and day out. End of the day, they are not eating ENOUGH! I have yet to have even ONE young guy (as in 16-24 - the age of most guys asking me for advice) to even remotely be in the ballpark of what they CLAIM they are taking in cals-wise.
2 - So lets say you ARE that 1% that IS eating the cals of what you claim. And yet, you STILL aren't gaining. Then guess what - ready for it? You gotta eat MORE! Math doesn't lie young brother - if you aren't gaining scale weight, then you have to eat more. Does that mean you only eat when you are hungry? HECK NO! You want gains, you gotta work for it dude - and that doesn't mean just in the gym, that means 24/7/365. Eating right is prolly the hardest part of the game. Does that mean force-feeding, as in eating literally every 2 hours if need be? Does that mean eating when you're not hungry, and you're looking at that food like "Uuughhh"? Damn right!
I'm very happy that you posted that pic so we can all see how lean you are, bcoz that right there tells you the answer. To get bigger and stronger, you DON'T want to be that lean. At your age, your metabolism is kicking in high gear baby - I mean steam rolling. And to make up for that, you have to get in more cals. Are you going to gain some fat too? OF COURSE! That's part of the game of getting big. Ronnie Coleman, Dorian Yates, Jay Cutler - do you think these guys were lean during the off season when they are trying to grow and put on muscle mass? Heck no man. None of the greats, or even not-so-greats, are even remotely as lean as you are when attempting to put on size.
If you can't put on size now, natural, then if you do a cycle, you will be one depressed mofo when you see the gains aren't even a fraction of what you expected, simply bcoz you don't know how to eat right. You're 6'0 tall and only weigh 160 lbs. Helluva improvement of when you weighed 100, but you look to be sub-10% bodyfat. You need to start eating more until you start seeing that scale go up. You can easily put on another 40 lbs (minimum) from eating more and training heavy on all the Mac Daddy, proven movements, ie, squat, deads, bench, bent over rows, military press, pullups, dips, barbell curls, skullcrushers. You should pay someone to beat your ass if you as so much even look at a cable crossover machine on chest day, or a cable curl on arm day. The BASIC exercises, eat MORE MORE MORE, get your bodyfat levels UP. Forget about eating all super healthy and strict - yeah get your protein in via chicken, beef, eggs, milk, but also get them cals in via pizza, pasta, potatoes, ice cream blah blah. Do what you must to get the scale MOVING amigo.
Being this all comes down to getting in more cals, you also want to stop doing ANYTHING unnecessary that burns cals. No cardio, no basketball, NOTHING thats going to burn cals outside of killing the heavy weights in the gym dude. If you got a girlfriend and she wants sex 3 times a day, then tell her to get on top so SHE's burning all the cals!
Finally, if you want a "secret", here it is. Peanut butter (PB)! That's right. I advise any young brother who hits me up in the gym who wants to get bigger, to start eating peanut butter. That doesn't mean to substitute one of your regular meals for it. You are going to use PB as a SUPPLEMENT! Why PB you ask? Here's why - PB is prolly THEE most calorie dense food you can eat gram for gram. One normal size jar of PB has 2800 cals, 112 grams of protein, 224 grams of HEALTHY fats, AND it costs less than $3! PB should be in everyone's arsenal if they are trying to put on size. I would advise you to eat 5 tablespoons of PB right before you go to bed to sleep, along with a large glass of milk. If you don't like to eat it straight off the spoon, then heck, make it into a couple PB sandwiches. Be consistent, do this EVERY night.
That's the answer dude. You do what I say, and start growing. EAT EAT EAT. Force feed if need be. Hit it heavy and hard on the basic exercises, get a lot of rest & sleep, lay off any calorie burning activities, and GROW!