The last eruption was in El Chinyero, near Santiago del Teide in 1909.
Previous eruptions in Tenerife, have as you say, happened approx every 100 years or so.
It is human nature to look for patterns in everything, but as volcanoes do not have access to calendars or clocks, they cannot be in any way predictable.
Mount Teide has probably more monitor sensors than any other volcano in Spain, so if there is any increased activity it will be detected in an instant, which is intended to act as a warning of any future event.
Mount Teide is classified as a decade volcano, but i worry more about being run over by a bus.(being driven by Lord Lucan)