I got my first testosterone test along with my STD test in December.  I'm almost 69 years old now.  My testosterone level was good for my age, but obviously not like a young man anymore.  I happen to read that boron can help increase the amount of free testosterone from total testosterone.  
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So I've been taking boron supplements for the last couple weeks.  Plus zinc and vitamin-d. The last two more for covid prevention.
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Anyhow I met a SB yesterday and usually I need mechanical stimulation to get a good hardon (I also take half a dose of viagra.)  Well this time I got an erection during foreplay without direct stimulation to my dick.  That's more like in youth when you could get stiffies just thinking about sex.  
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Not sure it was the boron, or just a fluke.  But I'll keep experimenting.  They do say to cycle on and off boron every few weeks, so I suppose I should do that next.