For cruises like transatlantics and transpacifics, because they are longer and usually at times when kids are in school, they tend to be less rowdy or party filled, even on lines that might typically be a bit more lively. For example my first transatlantic was on Royal Caribbean, a mass market line that markets heavily to families. I would say the average age on the ship that cruise was in the low 70s, and that is not atypical for a long, one-way cruise.

Because transpacifics are not as common as transatlantics, especially northern transpacifics (which is what you want), your selection may be limited.

At that point it comes down to amenities on ships, size of ships, and cost.

Instead of choosing a cruiseline first, I would take a look at what is available in your desired time period, then ask about specific cruises and ships.

For time periods to look at, you are most likely to see a transpacific in the direction you want in April-June.