I will speak to them in English only [once they turn 3]. (First sentence can by trimmed down a bit. "years old" isn't needed, and "onwards from" is covered by "once" is this case.) I had my mid term exam [for my] university class ("in" here would be the physical class location, while "for" mean "associated with" which I think you want). I finished early and asked the teacher if I could leave under the pretext that I had some business to do. She said I could go on condition that I went downstairs to have my power point slides printed out and brought [to her] (PP slides can't be referenced as "them" this way - you can check to see if it makes sense by removing additional verb clauses. Try reading the sentence out loud without "printed out and" - it should sound better without "them", and the structure should stay when adding additional verb clauses). I agreed[,] walked out of the room [] towards the stairs and [] went downstairs (multiple actions or lists work better as commas than repeated "ands"; "I" doesn't need to be repeated). I pulled out my phone to check the time only to realize I would be 10 minutes late for work if I didn't leave. Here I am now, headed to the metro station, where I will take the train to work. If I miss the one pulling into the station, it won[']t be a big deal[, as] they [arrive] every 5 minutes (the two final sentences are correct, but because the second one explains the reason for the previous one, it sounds more natural to connect them. Instead of "as" you can also say "because", or even use a colon) ("draw in an out" works, but arrive sounds more natural, especially since the act or arriving is the focus, not the departing, and it matches the use of "pulling in" from before, also focusing only on arrival). (This is a very solid piece, and easy to follow. Even without the changes it is very clear!)