American support for gay marriage is at an all-time high, according to a new Gallup poll. 

Gallup, which has been following the issue for almost 20 years, reports that 55 percent of Americans now support same-sex marriage. 

While support for gay marriage has been increasing for years, it only rose above the majority in 2011.

According to Gallup's new poll, young Americans support gay marriage more than older Americans, with 78 percent of Americans between ages 18-29 believing that gay marriage should be legal in all 50 states. Only 42 percent of Americans over 65 think gay marriage should be legal. 

In terms of political alignment, Democrats are more likely to support same-sex marriage than their Republican counterparts, with 74 percent of Democrats believing in marriage equality, compared to 30 percent of Republicans. The majority of Independents also support marriage equality, with 58 percent believing same-sex marriage should be legalized. 

When Gallup first conducted a poll about gay marriage in 1996, 68 percent were opposed, with only 27 percent supporting marriage equality. Since then, support has steadily grown, reaching 42 percent when Massachusetts became the first state to legalize same-sex marriage in 2004.

Eighteen states and the District of Colombia have legalized gay marriage, with more and more states striking down bans on same-sex marriage. States have been ruling against gay marriage bans since the Defense of Marriage Act was struck down by the Supreme Court last year. 

Pennsylvania's ban on gay marriage was ruled as unconstitutional on Tuesday, following similar rulings in Oregon and Arkansas earlier this month. 

Federal judges have also struck down gay marriage bans in Oklahoma, Idaho, Virginia, Michigan, Utah and Texas. While many Republican lawmakers in the states are appealing the rulings, no ban on same-sex marriage has survived a court challenge since June. 

Most Southern states still have constitutional bans on same-sex marriage, although the ban has been challenged in Kentucky.