Hi there. Yes, caste settings are exactly what need to be examined and adjusted here. You will already have a caste for each of the various age groups, but if any are missing then it's not really difficult to create them.
On City Hall or an in-game computer, pull up NRaas > SP > Caste Options > Young Adults (to start out), look for Romance: Allow Partner Caste, and set the castes that you wish these sims to be able to partner with (so that would be I guess Young Adults and Adults). Alternatively, but you don't need to do both things, use Romance: Disallow Partner Caste to disallow partnerships forming with Elders. If you allow Teen-Older romance by way of Woohooer, then the Teenager caste would also have to be accounted for one way or another. Then look at Flirt: Allow Caste (or Disallow Caste) if you wish to limit flirting without partnerships forming as well. And then repeat for Adults and Elders (and Teens if relevant).
Note that the above really dictate what SP itself can do, so it is still possible that
some YA-Elder relationships may form. And of course sometimes when two Adults are in a relationship already, one of them will age up to Elder far sooner than the other. But without the restrictions in place, the game and the mod have little reason to avoid these kinds of couplings. For more info on how SP's Romance Manager works generally, we have this FAQ:
StoryProgression-FAQ-Romance
Overwatch can be used to export any or all NRaas mods settings in one step and then import them into another game, selectively or also all at once in one step. NRaas > SP > Overwatch > Immediate > Export (or Import) Settings. It can be helpful to name the Export appropriately such as "Bridgeport 12-14-19" or something like that so that if/when you end up with many sets of exported settings you will know which are which. The actual settings file lands in your game folder's Library sub-folder and will show up as a saved household with a generic icon in Edit Town, but the only thing you can do from there is delete it.
