The graduation was in 1989. Andy and Loli had sex and gave birth to Martín. All the series take place 19 years afterwards, when Martín is 18. But then... it is not taking place in 2012, but in 2008.
There is a thing that makes little sense: the romance of Patricia and Pablo. Patricia is actually Jimena Benítez, the fat girl from the school, and although she had unpleasant scenes with most of the others, the worst of them all was Pablo. And now she loves him? Even having a son with him? There is a possible explanation. The son that Patricia is waiting, that she says it is from Pablo but tries to pass as a son of Clemente, is really the son of Clemente, with no deception on that part, and she knows that. She's just fooling Pablo. After all, Clemente has not been in High School with her, and never was mean to her; she has no reason to focus her revenge desires on him.