whole milk

when can i start to introduce whole milk? i've heard different answers from different people. i'm not planning on making a complete switch but was wondering when did you moms start mixing milk and formula. i have other mom friends who started at 8 months and others who didn't take their child off of formula until 1 1/2 years old. i've also heard that you should wait until around one but was curious as to what y'all did and how it worked out! thanks in advance