Hi and welcome, these are the classic signs of a hemorrhoid. When you strain you force blood into the thin tissues of your anus causing a ballon type of reaction. When you strain the balloned tissues pops and the blood comes out. A person is never to young to get hemorrhoids. Its not a serious condition and most people in the world have them. Do you have an itching in that area? You might want to have a doc check this out to make sure your in good health.
If you're constipated and having to strain to poop, you can tear your anus a little bit, which will bleed a little. Bright red blood means it's coming from low in the intestinal tract, because blood from higher up turns black or tar-like, because it gets digested in transit.
To fix this, make sure you drink plenty of water, and get plenty of fiber. Fruits (other than apples and bananas) are an excellent source of fiber. Prunes, raisins, dried apricots, etc. with lots of water are good if you don't feel like fresh fruit. Whole grain products are also good. You can also buy things like benefiber or metamucil to add to your diet (I like the generic benefiber I have, because it really doesn't taste or feel like anything). You mix some in your drink a few times a day and voila!