+-----+-----+
       |  A  |     |
 +-----+-----+-----+
 |  B  |     |      
 +-----+-----+

The ages of Ambrose, Brandon and Chester can be related to the diagram above so that when just one digit is written in each box:

1. A across is Ambrose's age in years.
2. A down is the sum of Ambrose's and Brandon's age in years.
3. B across is the sum of Ambrose's age, Brandon's age and Chester's age in years.
4. Two of Ambrose, Brandon and Chester are the same age in years.

Who is a different age in years from the other two?