I want to ask you a question. Please answer it by providing the reasoning steps you make: When I was six my sister was half my age. Now I'm 70, how old is my sister?
When you where six your sister was 3 years old.
Which means that your sister is 3 years younger than you.
Now you are 70, and because your sister is 3 years younger than you your sister is 67.
However it depends when you are born and when your sister is born it might be that your sister is 68 if your sister already had her birthday for the year and you did not. Opposite if your sister did not have her birthday for the year but you had yours she would be still 66.
Can you write that with better grammar and spelling? I'm struggling to understand it.
When you were six years old, your sister was three years old. 
This means that your sister is three years younger than you. 
Now that you are 70, your sister is 67 years old, considering the same birth year. 
However, the actual age of your sister might be different, depending on the exact birthdates of both of you. 
For instance, if your sister has already had her birthday for the year and you haven't, then she would be 68. 
On the other hand, if she hasn't had her birthday for the year, but you have, then she would still be 66.