Also consider that production time may vary greatly from release of the movie or airing of the episode. Timeline issues sometimes make this more apparent, as 5 seasons of a tv show may only cover one year within the context of the story, making an actor who was an aversion become a straight example over time.Consider also that the exact age of the may also be in question (a generic "high schooler" can be anywhere from 14 to 19).This ought to be horribly distracting, but by and large, television audiences have learned to manage.It is so ingrained into our mindset that almost all aversions end up being notable.In March 2008, the International Telecommunications Union-Radio communications sector (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 100 megabits per second (Mbit/s) for high mobility communication (such as from trains and cars) and 1 gigabit per second (Gbit/s) for low mobility communication (such as pedestrians and stationary users).Since the first-release versions of Mobile Wi MAX and LTE support much less than 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded 4G by service providers.If younger, casting usually tries for children actors, and if older it is simply far less noticeable.If a show or movie carries a greater focus on the adults rather than the kids then they will usually avert this.
If anything finding a 19 year old to play a 17 year old is well ahead of the curve.
While maybe not the worst case example (Jack aside), it is a joke that has filtered into the cultural mindset regarding the show.
By and large this trope requires some research, you can't know for certain that an actor/actress is a certain age unless you scour around Wikipedia or IMDb.
It can sometimes result in a paradoxical effect: teens that look more like actual teens (either with real teenage actors or in animation) are described as looking "too young" (see Reality Is Unrealistic).
Conversely, actors in their early-to-mid-twenties, especially those who make their name in these kinds of shows, often have difficulty being taken seriously playing characters their own age.