NO, your age is NOT limiting you...you are. You are the in the beginning stages or the prime of your life, especially hormonally speaking.
You need to ask yourself some questions:
- What are your goals?
- Are you trying to build muscle mass?
- Are you training to build cardiovascular endurance?
- What time frame do you want to accomplish said goals?
- Does your exercise program support your goals?
- Does your diet support your goals?
These questions are important because they give you a compass, a direction, and something to work toward. Also, it gives you focus and perspective, you need to measure where you're at in your journey and where you want to end up. If you don't have a starting and ending point, you have no frame of reference for measurement. How do you know where you're going if you don't have a focused goal?
Stating that you eat considerably well by eating 4 meals a day and drinking protein shakes doesn't define anything or mean that you actually "are" eating well. Again, how do you know if you don't measure? How do you know if your diet is well enough to support your goals?
Also, when you say that you workout...what does that mean? Are you on a program? Are you performing specific exercises every day that you workout? Do you keep a training log? This is important so you know where you have been and what to do better the next time you perform those set of exercises.
For an example, with some quick math, and a general starting point for building muscle mass:
- 65.5 KG (144 lbs)
- 14% bf
56 KG (124 lbs) of Lean body mass (LBM)
1586 kcals - Basal metabolic rate (BMR)
- 2142 kcals - Total daily energy expenditure (TDEE)
2356 kcals - Daily caloric intake (TDEE + 10% of TDEE)
144 grams of protein
- 327 grams of carbs
- 52 grams of fat
These numbers are based on 4-6 hours of exercise a week. If you workout more or your metabolism (this is subjective) is faster than average, then you need to increase your caloric intake. You can get an idea of how well this diet is working by getting an average of your weight over 7-10 days. If it isn't going up, then you add calories until it does. Weigh yourself every day after going to the bathroom and keep an average. You need a data point for comparison or you don't know if your changes are working. Realize that weight gain isn't necessarily always linear, it'll look like a stock market graph if you put your daily weight in a spreadsheet.
If you need to add calories, do so at 50-100 kcals at a time, then wait for 7-10 days to see if your weight climbs. Add calories to carbs and fat first, then consider protein later. Typically, you'll want 1.1 to 1.3 grams of protein per pound of lean body mass - there is much debate over this topic.
The above coupled with a proper weight training program will yield incredible results at your age between now and high school graduation.