I could never hear 20 kHz, even as a kid. I could hear up to around 17 kHz in my 30s, and now the highest I can hear as a pure sine wave is 14k with my right ear and 13k with my left. As for lows, I can hear down to around 17 Hz - I don't think it's the 34 Hz harmonic because it's on LCD-2F headphones which have very low bass distortion. From what I read for age 55 I am fortunate.
What's strange is when I test my HF hearing in a different way, by applying low pass filters to high quality recordings of jangling keys or castanets, having lots of energy at 20 kHz and higher, I can detect a low pass filter with a slightly higher cutoff frequency than I can hear as a pure tone. I can detect how it smears the crispness of transients, even though I can't hear it as a sin wave. For example I can detect the low pass filter with a cutoff of 15k, which I can't hear as a pure tone. Is that because the slope of the cutoff filter isn't steep enough, or is it because our ears are non-linear devices that are not symmetric in the time & frequency domains?