1.When did you buy it ?
=> How long have you bought ?
2.I started / begun studying English 3 years ago.
=> I have studied English for 3 years.
3.I last saw him when I was a student.
=> I haven't seen him since I was a student.
4.The last time she went out with him was two years ago.
=> She hasn't gone out with him for two years.
5.It's ten years since I last met him.
=> I haven't met him for ten years.