VERY generally speaking, 20s are warm, 30s are hot. Humidity changes this a lot. And yes, personal sensitivity to heat plays a role. I live in a dry climate, and I feel rather comfortable until we’re close to 30 ºC. I remember reading something like the ideal room temperature for humans was around 20-22 ºC.
For those using F, this is, more or less, the scale of C:
Below 0: freezing (0 ºC being the freezing point of water, duh!)
0 to 10: cold (don’t go out without a coat)
10s: cool (a sweatshirt or light coat may do)
20s: warm
30s: hot
40s: uncomfortably hot (stay in the shade and hydrate)
50s: you’re dead (or you wish you were. Unsafe for humans)