There is a genetic contribution, but it is not determinative. There are a lot of factors. Your son is at a higher risk than an average kid without family history, but still, there is a much higher likelihood that he WON'T develop bipolar.

The age range for diagnosis varies tremendously.

The presentation and symptomatology also differ from person to person, providing kaleidoscopic variety.

Bipolar is notoriously difficult to diagnose in adolescents because moodiness is a normal characteristic of that age group and drawing the line between teenage angst and depression or teenage rebellion and hypomania is extremely difficult.

I think you are lucky that you have a son - if he develops bipolar and ever needs medication, the choice between getting pregnant and not treating the bipolar or treating the bipolar with teratogenic drugs and not getting pregnant would not be relevant for him. This is a huge relief for you.

You also need to be vigilant enough for signs of depression during adolescence. If such signs develop, and your son sees a dr, that dr MUST know that the dad has bipolar, because giving Antidepressants (AD's) alone to a teen with a family history of bipolar is dangerous. AD's are sooooo commonly given to teens today, and by whom? By family doctors without psychiatric expertise... so AD's could flip your son into mania. That is more or less the most important precaution for you to keep in mind. Better yet, if your son ever develops any kind of problem remotely implicating anxiety or mood disorder, do not talk to family physician other than to ask for referrals. Get a psychiatrist with an adolescent sub-specialty help your son.

Other than that, regular and sufficient sleep, life with recurrent activities, not too much stress, not too many AP classes, etc. - avoid psychosocial triggers that may set in motion what otherwise can remain dormant for life.

Enough sleep and moderate exercise would be very helpful. If you can model it rather than "make" him do this, you'd be a superwoman .