As I recall, madman pointed out that there are flaws in the studies coming up with the longer half-life. When corrected they also point to ~5 days as the half-life. I would stick with this figure.
The equation uses time after peak, not time before, with the peak occurring right at zero time:
T(time_after_peak) = Peak * exp(-ln(2) / half_life * time_after_peak)
The model just assumes a pure exponential decay after the peak serum level is reached.
I'd been thinking it's longer, but it seems to be around a week.
Your first two measurements give a reasonable half-life of 23 days. The final measurement is indeed much higher than if there were a continued exponential decay. This just shows the shortcomings of the model and/or a measurement anomaly.
If we assume a one-week post-injection delay to peak then we can work backwards using your 23-day half-life to find that your peak testosterone is estimated to be 2,200 ng/dL.
