Great question, and I hear the worry in your writing. I have a couple thoughts about the situation:
(1) If your son is on the verge of a thought disorder (like schizophrenia), then what are called the "negative" symptoms would just be rearing up around this time in his life. The withdrawal, odd emotional patterns, and poor hygiene would not necessarily have been present prior to the past year or so. Any earlier, and it would have been a rare, early onset.
(2) If these symptoms were always present with your son, he may instead be suffering with a condition called Asperger's Syndrome. These kids tend to be intelligent cognitively, but rather poor interpersonally (socially). They tend to get absorbed in things (like computers, for example), and over-learn the things they are fond of.
(3) Back to schizophrenia for a moment... even if he does not develop full-blown schizophrenia, there is another condition called schizophreniform disorder whereby the person goes through the same phases, but without the extreme disruptions of schizophrenia. In other words, the odd thought patterns and hallucinations and/or delusions are not nearly as pronounced, nor is the level of impairment.
Given that his grandfather had schizophrenia, your concerns are quite justified. My advice would be to have him evaluated sooner rather than later. As you know, once the florid ("positive") symptoms flare up - and the schizophrenia/schizophreniform disorder moves into the active phase - the patient does not think they have a problem and will therefore become extremely resistant toward treatment. Better to start the process while he is still cooperative. If the counselor is too busy for you, get another one. Too, a psychiatrist may be called for the evaluation, as medication is sometimes a good treatment option.
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