Usually between the ages of 30 and 35 male testosterone levels begin to decline by about 1 percent per year. However there are several things that can be done to counteract that natural decline and actually raise them. Primarily they have to do with diet and exercise.
Regarding diet, be aware that cholesterol is the precursor of testosterone and therefore is absolutely necessary for the body to increase its production. Two excellent food sources of cholesterol for that purpose are eggs (the yolks) and butter. Two eggs and two tabs (1/8 to 1/4 inch thick each) from a stick of butter should be sufficient. To ensure proper digestion and absorption you may want to include a good digestive enzyme supplement with your meal.
Also be aware that as natural testosterone levels in men begin to decline after the age of 30, natural estrogen levels, which had always been significantly lower than testosterone levels, begin to increase. To counteract that increase, include one or more cruciferous vegetables (from the cabbage family) in your diet. Broccoli is excellent for that purpose.
Regarding exercise, the emphasis should be on strength training with moderate to heavy weights every other day or at least twice a week and/or what is known as HIIT, which stands for high intensity interval training. Repetitive wind sprints - running at top speed for about 40 yards, resting for one to two minutes and then repeating for 20 to 40 such intervals, or doing the same on a treadmill for 40 to 60 strides, resting, and repeating, etc. will produce results, particularly when combined with the dietary modifications.
There are several excellent articles on the subject available on the internet.
The following is a brief excerpt from one of them.
"
How to Increase Testosterone Naturally
1.
Eat a well balanced diet. Put an emphasis on foods with
high saturated fats like butter, coconut, eggs.
2.
Supplement with Vitamin D3, fish oil, whey protein, and
magnesium!
3.
Exercise With an emphasis on strength training and HIIT cardio.
4.
Don't overtrain!
5.
Get more and better sleep.
6.
Manage stress.
7.
Avoid Xenoestrogens and Other T-Lowering Chemicals.
8.
Have more sex.
9.
Take cold showers (maybe)."
Click the following Link to read the entire article, entitled "
Testosterone Week: How I Doubled My Testosterone Levels Naturally and You Can Too
https://www.artofmanliness.com/2013/01/18/how-to-increase-testosterone-naturally
The following articles are also excellent.
5 Foods to Boost Your Testosterone by Ken Swearengen at
https://myhealthwire.com/news/menshealth/428
9 Tasty Foods that Give you More Testosterone Naturally by Ali Kuoppala at
https://www.anabolicmen.com/best-testosterone-boosting-foods
7 Smart Ways To Boost Your Testosterone by Alex Savva at
https://www.bodybuilding.com/fun/7-smart-ways-to-boost-your-testosterone.html
And finally this one from a well known medical authority on the internet, Dr. Mercola:
9 Body Hacks to Naturally Increase Testosterone at
https://fitness.mercola.com/sites/fitness/archive/2012/07/27/increase-testosterone-levels.aspx