Some studies show increases in IQ over the decades, and that is consistent with my own suspician that high school and grammar school students hold their own quite well with generations past.  Possibly, with a sample of therapy clients, the verbal abilities may be higher than the general population. Or, possibly my own entrenched ideas, with a poor expectations of high school students may have something to do with that impression. And finally, I do really hope that it is not do to my own declining abilities as decade succeeds decade--said in jest.  The stereotype is of oldsters ragging on the  the new generations and their deficiencies of learning, and this just is not permissible anymore. This generation of high school students speak with relative ease about things submerged culturally in the past, and are conversant with things it took me years to learn in the befuddled, distant, and dimwitted era in which I was raised.  Exposed to liberating and stimulating environments, teens now seem to be able to talk with relative ease about identity, anxiety, subtleties of relationships, and parent divorce with the clinically cheerful quality of an 1980s grad student.  This is not the same as increased reasoning or cognitive abilities, but those too seem better than I remembered at the time,  I speak with adolescents in my work and family activities. Across the board they seem just smarter than we were, and frighteningly, encroaching on my long developed perspicacity. There is even a name for this purported even--The Flynn Effect.

There is one area that teens seem weaker than their baby boomer grandparents, and that is in classical knowledge. Understanding of history and literature seem undeveloped although perhaps compensated by improvements in mathematical and STEM areas.  References to events in history or literature before 1950 or 1900 seem weak, and distorted--possibly there is less immersion on old knowledge because new knowledge arises geyser like every time a laptop is opened.

Certain types of intelligence peaks at certain times. Mathematicians tend to be young, politicians flourish at the other end of the age spectrum, and for the pursuits that require idealism--activism for example, youth also is important. Psychological knowledge seems not to require long apprenticeship anymore, no more a result of long experience and wisdom but just immersion in the ocean of information on the web. Clients often know as much as their therapist. The old job of psychologist was to explain diagnosis and provide treatment. Nowadays there is a more collegial aspect to the therapy process because its hard really to tell many clients anything. They have access, with their younger  brains and brand new short term memory,  and modern electronic tools and databases, to the same information the therapist has., and the information is more freshly learned. Probably the area that an older person has an edge are seeing deviations from patterns. Having been exposed to occasional black swans, as the term goes, there is better alertness to the odd event, the unusual diagnosis, the case that does not fit the usual outlines 

People learn from experience. Yes, true enough, but at the same time people learn all the wrong things for experience. Half of what is learned is likely to be wrongheaded or effected by the brain of the person who invented it.  Lets put it this way, you learn something from an experience but whether what you learn is useful, accurate, or really an advance on what you thought before is unclear. At times, better not to learn from experience, to avoid being hardened, changed or affected by a single event that may or may not be characteristic of a situation.  Don't learn anything and at least you keep an open mind, uncluttered with useless pseudo-knowledge.

I would say the one other area that older people have over younger people intellectually is that, being better off financially, decisions can be more detached, or developed in a more quietistic environment. A doctor in their thirties scrambling hyperactively around to pay bills or make his mark financially or professionally, is bound to be rushed, compared to the circumspection of a more placid 50 year old doctor less possessed by anxiety and careerism. So, age has an advantage there. Overall, however, except in areas like politics where connections and seniority play a role, really the race for intellectual acumen goes to the younger. Rimbaud, the French poet and friend of the poet Verlaine, wrote his best prose as a teen. His mind was especially limber at that age--full of the grandiose joy of making poetry.  At about age 18 he ran off to Abyssinia to smuggle guns, or some such pursuit,  and possibly at some instinctual level he realized adulthood would not be the creative playground he enjoyed in his youth.