56. He hasn't chatted with his classmates through the internet for ages.

⇒ It's age since he last chatted with his classmates through the internet.

31. They started building the bridge two years ago. 

⇒ They have built the bridge for two years

32. Mai commenced writing the lesson twenty minutes ago. 

⇒ Mai has writed the lessons twenty minutes ago 

33. My Vi began counting her lucky money five minutes ago.

⇒ My Vi has counted her lucky money five minutes ago 

34. You started flirting with me forty minutes ago. 

⇒ You have flirted with me forty minutes ago

35. She began listening to the music fifteen minutes ago. 

⇒ She has listened to the music since fifteen minutes

`⇒`

`56.` It's age since he last chatted with his classmates through the internet.

`31.`They have checked the machines for two hours

`32.`Mai has writed the lessons twenty minutes ago

`33.`My Vi has counted my lucky money 5 minutes ago

`34.` You have flirted with me forty minutes ago

`35.` She has listened to the music since fifteen minutes