You likely don't. However most Boomers will be dead within 20 years which is how long I think it will take Bitcoin to become as mainstream as Paypal, twitter, or ebay.
I would like to see your source on the life expectancy of baby boomers. A more realistic figure for the
average life expectancy of a baby boomer is 30 years. That also means that a significant portion of the baby boomers will live well past age 80.
As to why a baby boomer should hold Bitcoin. Very simple. Holding a small portion of their retirement savings say even under 1% in Bitcoin can mean the difference between a comfortable retirement and retiring in poverty particularly should the stock market drop significantly.
By the way I am a baby boomer
I am not planning my retirement on the basis of dying in the next 20 years
I do hold Bitcoin
... and by the way I also backed up my wallet.dat among other places on a 5.25in floppy disk. A technology that was obsolete before most of the members of this forum were born!