it’s true , “les pics” means in here the highest , “les pics ” in franch has different meanning and it depends on the context , here are some meanings of “pics”

   les pics de pollution = pollution levels reach a peak
   les pics = Picinae (birds) 
   tomber à pic = coming in the right time 

in here means the peak of sms use is between 16 and 25

In most French speaking countries, “étudiants” is quite restricted, and refers to persons in a higher education cursus, like post-baccalaureate (Wikipedia source):

Dans la plupart des pays francophones, l’usage du mot étudiant est
encore plus restreint. Le plus couramment, il désigne les personnes
engagées dans un cursus d’enseignement supérieur.

In the initial text (“Selon une autre enquête…”), I see no mention of the word “étudiants”, while “étudiants” is in the question. Generally, students are awarded a baccalaureate around 17-18 years. So if the peak is around 16, “étudiants” text above 17-18 text at a lower rate than at 16. If you assume that the rate is almost steady, perhaps slowly decreasing, and falls above 25, then the trend is globally decreasing from 17-18 to above ages.

In that context, the answer would be true.

However, one could imagine that people text a lot at 16, stop texting between 17 and 22, then suddenly re-text a lot between 23 and 24 (but at a slower rate than at 16, because it is the peak), and stop texting again after 25.

Then the answer would be false, because students at 23 text more than students at 20.

So from a purely logical point of view, I have not enough information to true, so I’d say false: there could be counter-examples.

But languages are not about pure logic, more about global statistical trends. If something else in the text, or the global level of the test is about global understanding, without clever tricks to make you fail, I’d go for a “true“, at the end. The text says “une autre enquête”, which means that the first survey may carry additional information.