Verified answer

The ∆G° you find on data tables is, by convention, measured at 25 °C (273 K), because that's room temperature.

Instead of making thousands of data tables, you can just pick ∆G° from one of them, and then apply the formula you're using to find ∆G at 37 °C (285 K).

You must realize that temperature is NOT part of what constitutes "standard conditions." Standard conditions are 1 mol/L for concentration and 1.0 atm for pressure, and temperature isn't a part of it.

Tables are tabulated with standard values at usually one assigned temperature, that of 25C, but you could just as easily have standard ΔH and ΔS values at 35C, and another set of standard enthalpies and entropies at 50C. Again, the temperature is not part of what it means to be at standard conditions.

Finally, your prof used 25C because that is the temperature for the standard values of enthalpy and entropy in the table. He could just as easily have used 37C, because there is little change in ΔH and ΔS from 25C to 37C. But to be accurate, you would need a table of standard enthalpies and entropies at 37C. You probably won't find that.