None of my family has saved anything for retirement, so they will need to work until they are unable to work due to age or illness. We have saved aggressively and I should be able to retire at 55/DH at 59 if our savings continue to accrue at their current rate. If we tell them in advance, we will be labeled as a) "uppity" (which is the term they use for anything good that ever happens in our lives), or b) bragging, because even if we just let them know so they aren't blindsided by it, it'll be seen as throwing it in their faces.
So we will not tell them, just like we don't tell them anything else that happens in our lives.