At what age will symptoms of hypogonadism manifest in men?

Typically 40s & olde: Hypogonadism is medical speak for low testosterone. Symptoms are non-specific. In other words, you might have something else if you're depressed, can't think straight, no interest in sex, loss of erectile function, loss of muscle mass, increase in fat, etc. While this can occur in younger men, this constellation of symptoms increases in frequency in our 40s and older.