If my age is 70, but my wife is only 65 yrs old, who's age do they take to calculate the maximum loan amount for a Reverse Mortgage?

Lenders always take the youngest applicant's age when calculating your Loan-to-Value-Ratio (LVR) for a Reverse Mortgage. In your case, they would take your wife's age of 65; then deduct 40; and use 25% LVR for the loan approval amount. On a $1.0M home, that Reverse Mortgage loan limit would be $250,000 (i.e. $1,000,000 x 25% = $250,000).