alignment - Input Field Widths

In a form with several input fields, is it better to define the same width for all fields (in order to maintain alignment), or to have different sizes for fields that are intended for less data?

For example:

Option 1:

 Last Name: [______________]
First Name: [______________]
       Age: [______________] <- this field is the same width as the rest even 
                                though it only supports 3 characters max. 

Option 2:

 Last Name: [______________]
First Name: [______________]
       Age: [__] <- this field is smaller and thus alignment with the rest is lost.

Which one is preferable? Keep in mind most of my forms will have at least 10 fields arranged in 2 columns, and maybe only 2 or 3 of them are going to be numeric or otherwise limited input fields.

Answer

Fields should generally be an appropriate size for their expected input, which may well mean that one field in a form has a different width to another field. The size of a field provides a useful clue about the information that should be entered into it. For example, if you're asking a user to input a postcode/zip, a field that is 20 characters long would be confusing because it creates the impression that you expect the user to enter something 20 characters long.