I would say, its not so much hatred but misunderstanding and bad stereotypes for older people. You see America idolizes youth and demoralizes old age. You see those commercials with the old people that fallen and can't get up. They make old people look like pathetic victims that can't take care of themselves and whose only real value comes after death when their family members can cash in the deceased insurance policies. That sounds really evil, but those damn commercials are really disrespectful to older people.
America is very capitalistic and there is a market for everyone, and older people get the short end of the stick because they don't have much spending power (not as much as younger people). Older adults are retired and don't have much income, so companies market their age as a way to make $ from them.
Moving on no-one wants to age (even though it is seen as a blessing and a privilege). The older you get the closer to death you are. People fear the unknown (aka change and death). I guess older people can be seen as reminders of death and just like sad people, people don't want to be around death either.
Lastly older people are isolated from society. The newer generations are in control and older people are often put aside because oftentimes people view them as useless, non-contributing members of society. Isolated by sickness and the fact that they can't relate to the newer generations. Older adults don't watch the same shows movies, don't listen to the music, don't understand technology as the newer generations. There is a real disconnect and not much in common.
I would say some older people can be cynical, bitter, and resentful and they think a lot of young people don't know anything. While young people think they are invincible. Most of that is stereotypes BUT knowledge is power. Older people have experience and younger generations have technology, both are KNOWLEDGE AND POWER!!! Both members are the opposite ends of the age spectrum should appreciate and listen to each others knowledge.
Anyway aging is special and that people are useful and valuable at whatever age! Hopefully businesses, advertisers/marketers will lay off that old people bashing commercials