Youth is a way to collectively refer to all people below the age of adulthood, and sometimes also to people who have just only passed the age of adulthood because the standards of who is an adult vary worldwide. In a general sense, youth refers to people aged 0 to 18, and sometimes also includes somewhat older demographics depending on local culture, education, social class, and other factors. To refer to people aged 0-13, use children. To refer to youth in the transitory stage between child and adult at age 12-19, use teenager. To refer to older youth that may be considered legally (but not socially) adults, and may even already be financially independent at age 18-21, use young adult. Each of these categories overlaps; transitions between them are not harshly defined.
Policies, social attitudes, behavior, and speech that marginalizes or restricts the already-limited agency of youth can be considered ageist.
Characteristics of intersectional youth experience
It's generally assumed ideal that people included under the youth label would be under the care of at least one parent or other legal guardian, making them legal dependents. However, this is not always possible; independent minors exist, homeless youth exist, and youth in foster care exist. Also, what may be considered "youth" can sometimes fall beyond the age of legal dependence; young people in college or their older youth peers, despite being over 18, may also be considered simultaneously youth and "adult," and may not be assumed to be in the care of a guardian.
Because youth are commonly dependents, they are at risk for parental or guardian abuse because under a certain age they do not have legal agency, and even over that age they may be stuck depending on an established, but abusive household to survive.
Because of current societal norms, children are often gendered at birth. Because of the amount of power their parents and expectations they may have for their child, coming out for queer or trans youth may be difficult or hazardous-- resulting in a statistically significant amount of trans and queer homeless youth.
Youth are often discouraged from appearing in public or having sufficient outlets to play, explore, or otherwise just exist. Anti-loitering laws, anti-play laws (such as against skateboard, wall-ball, or other activities) and removal of public rest infrastructure such as benches, kid-friendly/"dry" venues, and gentrification of malls effects where youth can make a space. While many areas devote areas to public parks and playgrounds, this does not help youth of all ages have safe spaces.
Youth can be considered a demographic of constant social concern, though "protection" of youth does not translate to an increase in agency but instead often a decrease in agency. Media targeting youth is also targeted at parents' and guardians' sensibilities in "what's appropriate" for their children (sometimes legitimate, as a trigger warning, sometimes less legitimate, as censorship), and the quality of said media is hotly debated on grounds of inclusiveness, violence, sexuality, and other topics. Safety for youth is may be regulated as well as diet (in public institutions and some private establishments such as summer camps) and education, where applicable.
Violence against youth, who are typified as having less power, or as less able to defend themselves as well as adults, is often considered an atrocity, though depending on the privilege of the victim the power of social outcry will vary.
Youth and education
Education in particular is framed to prepare youth for their future adult lives and provide an alternative to work for youth to engage in during most days, where it is provided. The quality of, and credentials provided by, this education depends heavily on race, social class, and geographical location.
However, because education is a system like any other, the extent to which even good education prepares children for increasingly competitive jobs in many countries is up to debate; where youth will later work is often dictated by privilege more than academic excellence. Topics such as grade inflation and privatization of education may also be topics relevant to youth, as well as college admittance.
Youth and labor
Child labor laws exist in many places in the world to state a minimum employable age, encouraging parents to send their youth to school rather than use younger children to help support the household. Many youth over an age of employment are employed part-time in addition to their schooling, especially where youth demographics extend to include dependents over 18. though teen, young adult, and other legally employable youth face steep unemployment in many areas of the world, three times more than adults. 
However, these regulations do not exist everywhere, and subsistence without child labor in families is not possible everywhere. Youth in working poverty are exploited, as well as women, to work all over the world, especially where no regulations on youth labor exists. Child labor, including child sex labor, accounts for a large amount of human trafficking.