I have always hated when people write things like:
Today is John Lennon's 75th birthday
No, no, a thousand times NO!
When people die, they stop aging. That's part of the point of death. John Lennon will never be older than 40. John Kennedy will never by older than 46. Marilyn Monroe will never be older than 36.
Attaching an age older than the age of a person at their death is just plain silly and it denies that they've died.
It is correct to say:
Today is 75th anniversary of John Lennon's birth
That acknowledges that time has passed since he was born, and that he is no longer with us.
Almost as bad is the all-too-common phrase
Today would have been John Lennon's 75th birthday.
Now, when a person dies fairly young, this is a common phrase, and it didn't start bothering me until recently. You expect when someone is murdered at 40, that they could very well have lived another 40 years or so more. But, somehow, once you start saying "X would have been 90" today, that gets much less likely. The vast majority of people don't live to be 90.
My tendency from now on will be to say:
Today could have been John Lennon's 75th birthday.
John Lennon could still have been hit by a bus or something at 41. Just because he was murdered young doesn't mean he would have lived to be very old.
I think acknowledging a dead person's birthday as "anniversary of their birth," while a little wordy, is much more accurate.
Finally, I really don't like the term "passed away," but I understand why people prefer to use it. It sounds less harsh than to say "died." But "died" is more accurate and more honest. So when I die, please say "Laurie has died." I haven't passed anywhere except into death.