Life expectancy from an estate planning perspective is only important when there time has expired. That said, assuming younger generations will outlive older generations isn’t necessarily true.
Take for example the life expectancy of a 40 year old person. Using 2000M actuary tables, that person is expected to live another 38 years. In other words, a person 40 years old is expected to live to 78. This might seem reasonable, until you compare this to a 75 year old person.
Again, using the 2000M mortality tables from Section 7520 of the Internal Revenue Code, a person that is 75 years old in 2021 is expected to live until their 86th season. Meaning, a 75 year old person might expect to have 8 more years of life than younger generations.
Of course, what this means to each person and family is going to be different. However, this is something to keep an eye on in the planning process.