Gravitational waves, predicted by Einstein in 1916, were first detected in 2015, ninety-nine years later.

True: gravitational waves were predicted by Einstein in 1916 and first directly detected in 2015 (LIGO, 14 September 2015), about 99 years later. Mostly true: the dates hold but the framing 'people looking' for 99 years is loose, since active searches began only decades after the prediction; treat this as a minor detail. Mixed: one of the dates is materially wrong. Mostly false: the first detection is placed in a substantially wrong year, or the gap is badly misstated while resting on the real LIGO detection. False: the evidence shows the first detection was not in 2015 and the prediction date is wrong.

Set before the research began.

1. E1 LIGO-P150914-v14: Observation of Gravitational Waves from a Binary Black Hole Merger LIGO Scientific Collaboration / LIGO Document Control Center

   “On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal.”

2. E2 Gravitational Waves Detected 100 Years After Einstein's Prediction | NASA Jet Propulsion Laboratory (JPL) NASA Jet Propulsion Laboratory · 11 February 2016

   “The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors”

3. E3 A century-old prediction confirmed: gravitational waves · Albert Einstein albert-einstein.info · 11 February 2016

   “Einstein had predicted these waves in 1916 but doubted they would ever be measured, since they stretch space by less than the width of a proton.”

4. E4 The long road towards evidence Max Planck Society (Blum, Lalli and Renn, MPI for the History of Science)

   “The first publication on gravitational waves within the general theory of relativity, entitled “Approximative Integration of the Field Equations of Gravitation,” was written by Albert Einstein and submitted on 22 June 1916 to the Prussian Academy of Sciences in Berlin.”

E3 and E4 show that Einstein predicted gravitational waves in 1916, and E4 dates his first paper on them to June 1916. E1 and E2 show that LIGO first detected them directly on 14 September 2015, which is about 99 years later. Both dates hold. The quote's wording, "ninety nine years of people looking," is loose phrasing; the evidence dates only the prediction and the detection, not when searches began. The criteria treat that as a minor detail, so this is mostly true rather than true.