I have spent a lot of time, over the past year or so, thinking about "adolescence." I've been trying to figure out how (and if) the term should be used to describe the people we're trying to describe when we use it.
Despite some recent work that's been done to try to suggest otherwise, the term "adolescence," in all its conceptual glory, is a new one (originating with G. Stanley Hall in 1904). Now, before you try to cite Aristotle or Chaucer to refute me, consider what is actually meant by the term, "adolescence." It doesn't just mean a specific group of people who are no longer children but not yet adults (or "emerging adults" or whatever comes next) or even just a time of transition between childhood and adulthood. "Adolescence" - since it entered the conversation as a categorical concept - constitutes a specific interpretation, a psychological and developmental discourse regarding the experiences of human beings who find themselves living under specific cultural, biological, familial, and political conditions. This is what we mean when we say that adolescence is a recent invention. It's not that these people didn't exist before 1904 and G. Stanley Hall created them (and Erik Erikson made them famous). Youth has always existed and the research suggests that it has constituted a distinct social space (or class) - distinct from both childhood and adulthood - in more than a few social contexts throughout history. But it didn't get interpreted through the psychological developmental lens of "adolescence" until recently. As we know it, developmental psychology itself, the discipline to which adolescence actually belongs, is itself a fairly recent phenomenon.
But I want to raise the question of whether or not "adolescence" is always the best word to describe the people we're talking about. Already in the question there is a potentially controversial implication that the people we're describing are people before they are "adolescents." The question itself calls us out of the pattern of using adolescence as a totalizing discourse. We're already moving away from allowing "adolescence" to close the case on these people's experience. "Adolescent" (even when we use it as a noun) is adjectival. We should not assume that every human being we meet, within a certain age spectrum, must fit the description explicated in developmental theories of adolescence. Instead, it only becomes helpful after we engage them as human beings and then decide to turn to psychological interpretations of their experience. But we need to be open to the possibility of turning somewhere other than psychology - other than "adolescence" - for our best understandings of these people.
I've been careful, so far, to avoid defining "these people" we're describing when we use the word "adolescents." I don't want to foreclose on the meaning of a person's experience by imposing my own categories. But I would like to suggest that, in taking an ethnographic approach to understanding them, we'd be better off using a term like "youth" or "young people." Because what we're trying to describe is not foremost "adolescence" (for reasons already addressed) in its psychological framework, but something like "youth" as a real cultural construction (even if its not as "recent" as adolescence), a social practice or social space that is distinct from adulthood and childhood in its symbols of meaning and social rituals. In other words, we're talking about "youth culture."
As annoyed as we may be by it, "youth culture" has been part of the Youth Ministry tool kit for a long time. But we've rarely (if at all) approached it the way we should approach a culture, avoiding ethnocentrism (or in this case, perhaps, "gerontocentrism") and operating on ethnographic principles without imposing developmental presuppositions.
"Youth," as opposed to "adolescence," is not a totalizing discourse. It does not carry with it a criteria to be met or a thesis to be proven. Instead, it allows us to interpret (not just translate) and find meaning in the social and cultural experience of occupying a unique social space. This helps us to avoid foreclosing on the meaning of such experiences by over-theorizing them prior to our encounter with them.
I could go on and on with why this is important for us as theologians... I hope it's obvious (but it probably isn't). But to put it simply, I'll appeal to Andrew Root's definition of the "theological turn in youth ministry." He writes, "A youth ministry that turns to the theological seeks to share in the concrete and lived experience of young people as the very place to share in the act and being of God" (see here). If we are committed to the idea that God is active in "concrete and lived experience," then we have to concern ourselves with discovering the most faithful understanding of that experience.... not simply for the sake of the experience, per se, but for the sake of participating in the life and being of the God whom we are experiencing.