Learn English – “When we X, we can then” vs. “we then can”

Because I'm older than she, I should be the first chosen.

I loved her and then she died.

If it rains, then it pours.

I've had more than enough.

Would you rather be a mouse than a rat?

Who, other than you, likes the color red?

When there is a comparison, you use than; then means:

1. at that time; at the time in question: I was living in Cairo then | [after preposition] Phoebe by then was exhausted | [as adjective] a hotel where the then prime minister, Margaret Thatcher, was staying.
2. after that; next; afterward: she won the first and then the second game.
   • also; in addition: I'm paid a generous salary, and then there's the money I've made at the races.
3. in that case; therefore: if you do what I tell you, then there's nothing to worry about | well, that's okay then.
   • used at the end of a sentence to emphasize an inference being drawn: so you're still here, then.
   • used to finish off a conversation: see you in an hour, then.

(See also the definition of then given in the Oxford Living Dictionaries.)

As you pointed out, the two sentences would typically be interpreted as having the same meaning.

A Scranton family has an average of 2.1 children.
The average Scranton family has 2.1 children.

The prototypical (average) family has 2.1 children. "The average family" in this case is a non-existent family, one whose properties are all equal to the statistical mean of the implied domain. This is a construct used for some statistical analysis.

The Jones are an average family.

The use of "average family" in this case means that this specific family is not an extraordinary case. Their properties are probably close to the statistical mean. However this is very much dependent on context. Perhaps the Jones are average with respect to income but not necessarily number of children. Using this phrase would not indicate that the Jones family has exactly 2.1 children.