I think Goldman is correct; the few truly bitter people I've met have been very elderly. Maybe it's because they have finally lost all hope, realizing that their lives really are not going to get any better. "My daughter always said that life sucks and then you die," a very unhappy 90-year-old said to me some years ago. "Turns out she was right."
If you have a friend or loved one who's struggling with bitterness, I trust you're sharing the answer with him or her -- the gospel of Jesus Christ, who has promised a joyful eternity to anyone who will repent and trust in Him to have paid their sin penalty on the cross.
A fresh look at what the Bible says about bitterness might help you make your case. Here to provide just that is an excellent message delivered by Chris Carrillo at Care-age of Brookfield's September Christian Music Hour.