1. Test for 'free testosterone level' and not overall testosterone level. Its the free roaming testosterone that does the magic. But at age 33 (I'm 32), our testosterone level has most certainly dropped.
2. Lose weight (that is if you're overweight) Testosterone converts to estrogen through the enzyme aromatase and the enzyme is found mainly in fat cells. These reduce the amount of free testosterone further. Also excessive estrogen has a negative effect on your libido and erection. A vicious cycle.
3. Take zinc supplement (as suggested above). Zinc inhibits aromatase activities. Zinc gluconate is by the most bio-available synthetic supplement otherwise, take lots of oyster. Be sure to check the RDA. Excessive amount of Zinc is toxic
4. Reduce or eliminate alcohol as it burden your liver's P450 function responsible for eliminating excessive estrogen among other things. Same goes for cigarettes.
5. Supplement to increase testosterone: Tongkat Ali is the best that there is bar none. Buy the pure root extract, extract strength at least 1:50, 400 mg per capsule. Its not cheap but its awesome (from personal experience). Another supplement to go for is Tribulus (haven't tried this though)
Finally, while testosterone is THE main male hormone responsible for sexual function (among other things), increasing the level of your NO->cGMP may be what you need to get an upright erection.
NO-Nitric Oxide is the pre-cursor of cGMP, the erectile dilator.
