T max is max OAT for given conditions. It is possible to have the reduced thrust setting, indicated with T flex, higher than this.
Setting T flex = 65°C, you are saying to the aircraft:
Hey, now please give me just as much thrust as you would be able to provide if it were this hot outside: 65°C. The maximum setting is determined by the 25 per cent requirement, hence it is not possible to set Tflex=85 because it would represent a larger thrust reduction than is allowed.
A1) The max flex setting is read from RTOW charts or obtained from PC performance calculation.
However, if it really was 65 degrees outside, you may not take-off. it is too hot. Maximum OAT for takeoff is usually lower than that. Tmax(OAT) <> Tmax(flex). The highest values for flex setting are pseudo-temperatures and only serve to set an appropriate level of engine thrust, real OAT for take off is limited by Tmax(OAT).
A2) T(flex) must be less than Tmax(flex) but once this condition is satisfied, T(flex) may be actually more than Tmax(OAT). Takeoff with OAT higher than Tmax(OAT) is prohibited.
FD (the un-real)