Obviously you get stretch marks when your underlying tissue, be it fat or muscle or a combination in most cases, grows faster than your skin will.
The opposite happens with sagging skin when you lose weight. The older you are, the less elastic the collagen will be in your skin.
Basically speaking, your perception of your body image and how fast you get there is not always in line with your genetics.
My advice is to take a look at your height for weight. If you're over your ideal weight, you're already near the limits of what you'll do naturally. Then, learn to accept the body you have as great instead of trying to always get bigger. It's the opposite of anorexia honestly, and bigger isn't always better. For one, your heart has to pump blood through a greater network of blood vessels, but you probably aren't training your heart if you're at that level of bulging muscles. So, your heart becomes less efficient at keeping your body oxygenated when you're bigger. I noticed this when I was around 180 and decided to lose weight. Now, instead of going for size of muscles, I just go for strength, which is not correlated much with size. The plus of it is that you actually improve your strength to size ratio, which is a mark of efficiency.
Obviously people on drugs will disagree with me. But this is my philosophy.