On draft day Trouba said education is important but will come once the Jets' give him the call.
Now for the speculation:
Due to NCAA rules Trouba can never attend a full training camp, nor can he play any exhibition games, or else he loses his NCAA status. This means the Jets will want to be sure he's ready as they can't have an "oh crap not quite there yet" moment. Also, for Trouba he'll have an incentive to stay at school unless he's on the team, as I doubt he'll want to leave school for AHL (especially when he noted education is important for him and his family, as stated above). So, he needs to be a guarantee really to make it, not just an iffy.
Tracking players with similar high acumen and similar development, the usual path would be:
*2 years of NCAA (including this season)
*1 year of either sheltered NHL mins and/or AHL leading minutes (more often NHL or combo, just AHL is rare for that high-end prospect at that stage)
*1 year of real role in NHL without sheltering
So, looking even at how he's been doing lately (WJC and all) he tracks for roster 2014-15 region... although development is never linear, ESPECIALLY with D, so I wouldn't be surprised if he took a year longer and IMO wouldn't mean any less of his ceiling.