Topic, in this case, is "Tema" not "Topico" (I think it´s better so the translation). Sometimes We translate word verbatim or literally (What is better? ) but the translation is fine (some words fail, like me with English XD)
The translation would be:
"¿Por que no encontré este tema antes? Tomé durante 4 años clases de Español y tuve mi ultima clase (que era una clase de AP ("Advanced Placement" may be?. I don´t know how to translate :-? ) ) el pasado semestre. Era muy difícil... Bueno, hubiera sido beneficioso si hubiera practicado aquí el español para clase, pero ya es tarde. "
In Spanish:
-The subject can be omitted in many sentences.
-The noun tells you the gender and number
-There are more tenses (8 in English (which I have studied) and 13 in Spanish)
What memories of my elementary school :-D !