The amount of defeatism in this thread would be humorous, if it weren't so pathetic. Yes, genes are important, but lifestyle is the other 30-40% of what decides your testosterone levels. Ill give you the short and sweet:
-Keep a healthy sleep schedule. You should be sleeping more during the winter because the days are shorter. As a rule of thumb, try to keep your day aligned with the natural light cycle. Of course sleeping 14 hours a day is not doable during the winter, but you get the idea.
-Absolutely no added sugar. This might be a little dramatic, but if you strive for no added sugar, you'll at least keep it below 20 grams or so a day. This lowers your body fat, which helps keep those T levels up.
-Similarly with refined grains like white bread, pasta ect. Whole grain is OK. Also, no beer.
-Veggies are you friends. Particularly things like broccoli, cauliflower, kale, ect.
-EXERCISE. This means a basic regiment that includes some cardio and lifting. You don't need to be going for gains. You don't even need to improve that much (unless you are really out of shape). Just get that cardio in and work the muscles. Don't forget to stretch.
-Last but not least, maintain a healthy social and sex life. Being intimate with a woman can DRAMATICALLY increase a mans testosterone levels, so get sexed up regularly, if possible.
The human body is a machine. Yes, the machines capabilities are determined when it is engineered (think genes), but keeping the machine oiled, supplied with high-quality fuel, and given routine maintenance sure helps...