why doesn't the rule of three work with age problems?

Question

For example:

When my sister was 7, I was twice her age. Now my sister is 13 years old. How old am I?

If you do

7  14

13  x

The answer is 26 but the correct answer to the problem is 20

when your sister was 7 then you were 14

so when your sister is 13 then you would be 20.

logic:

your sister: 7 years + 6 years =13 years.

you: 14 years +6 years= 20 years.

Answer 1

14/7=2

15/8=1.87

16/9=1.77

As time goes on; your % decreases.