Weighted Averages

// For all visible customers in the Customers
// dimension table the formula will calculate
// the age-weighted average income using
// only those customers that have supplied
// their age.

// Remember that a BLANK is treated as
// either '' (strings) or 0 (numbers),
// therefore the below is enough to get
// the weighted average.

[Age-Weighted Average Income] =
var __numerator =
	SUMX(
		Customers,
		Customers[Age] * Customers[Income]
	)
var __denominator = SUM( Customers[Age] )
var __avg =
	DIVIDE( __numerator, __denominator )
return
	__avg

And a mirror measure...

[Income-Weighted Average Age] =
var __numerator =
	SUMX(
		Customers,
		Customers[Age] * Customers[Income]
	)
var __denominator =	SUM( Customers[Income] )
var __avg =
	DIVIDE( __numerator, __denominator )
return
	__avg

Hope this helps.

Best

D