An adaptive wind turbine generator control system comprising - a measurement system comprising at least one sensor (A1, A2, MC) arranged to perform a plurality of measurements of a physical parameter indicative of mechanical vibrations of at least one mechanical component of the wind turbine generator at a plurality of operating conditions for the wind turbine generator, - a storage unit arranged to store, in a measurement database, data related to the plurality of measurements together with corresponding operating condition data for the wind turbine generator, and - an operating condition manager arranged to determine at least a rotor speed of the wind turbine generator according to a control algorithm in response to the data stored in the measurement database, - a resonance detector arranged to determine a rotor speed range in which operation of the wind turbine generator should be restricted, in response to the plurality of measurements of a physical parameter indicative of mechanical vibrations of at least one mechanical component, and wherein the storage unit is arranged to store data indicative of the rotor speed range in which operation of the wind turbine generator should be restricted, wherein the resonance detector is arranged to determine a rotor speed range where operation of the wind turbine generator should be restricted to avoid triggering mechanical resonances, in response to a comparison between a measure of vibration level or noise level and a threshold value (TH1, TH2, TH3), and characterized in that the control system is arranged to vary the threshold value (TH1, TH2, TH3) in response to time, so as to adapt an accepted vibration level of at least one mechanical component of the wind turbine generator in response to an age of the wind turbine generator. - a measurement system comprising at least one sensor (A1, A2, MC) arranged to perform a plurality of measurements of a physical parameter indicative of mechanical vibrations of at least one mechanical component of the wind turbine generator at a plurality of operating conditions for the wind turbine generator, - a storage unit arranged to store, in a measurement database, data related to the plurality of measurements together with corresponding operating condition data for the wind turbine generator, and - an operating condition manager arranged to determine at least a rotor speed of the wind turbine generator according to a control algorithm in response to the data stored in the measurement database, - a resonance detector arranged to determine a rotor speed range in which operation of the wind turbine generator should be restricted, in response to the plurality of measurements of a physical parameter indicative of mechanical vibrations of at least one mechanical component, and wherein the storage unit is arranged to store data indicative of the rotor speed range in which operation of the wind turbine generator should be restricted, wherein the resonance detector is arranged to determine a rotor speed range where operation of the wind turbine generator should be restricted to avoid triggering mechanical resonances, in response to a comparison between a measure of vibration level or noise level and a threshold value (TH1, TH2, TH3),