American Express CEO Steve Squeri told CNBC's Jim Cramer on Tuesday how the company attracted more Millennial and Gen Z customers, saying the cohort made up 60% of new card acquisitions during the last quarter.Squeri said American Express realized that attracting younger clientele was a "key thing" for the company, so it was important to offer cards with a high enough value proposition for that group. Younger card holders create a greater "lifetime value" than older ones, as they will continue to use their ...