Per FICO scoring know that AAoA is always rounded down to the nearest whole number though it'll never go below one year. So, your AAoA is 1 year now. I didn't look at your math either, but if you have 10 months, your AAoA will change from 1 year to two years in 14 months provided nothing is added or removed. Be sure to include closed accounts too if not already factored in.