We actually cruised both Lindblad on Nat Geo Venture in Alaska and NCL Haven on the Breakaway in the Caribbean in the past year.
While the Haven area was nice -- butler, concierge, lounge open all day, restaurant open for all meals including on port days for lunch, small pool, a hot tub, a covered deck, and a large sun deck -- my husband and I (60s) hated the cruise itself becuz: crowds and lines for everything. When conditions kept us from a port, we just ended up with another day at sea. My son (30) enjoyed the public hot tubs and lounges. The restaurants were so-so, even the specialty ones. There was plenty to do for the youngs, though.
Lindblad was fabulous in every possible way. The staterooms are tight, but the public areas are spacious and never felt crowded. Food was fabulous, staff was fabulous. Example: the hotel manager saw my husband come out of our room with a bag of laundry one morning and took it from him! The hotel manager! Entertainment was limited to evening lectures (what we saw today, what we'll see tomorrow), but they were interesting. When conditions weren't ideal, they pivoted to a plan B. There were multiple teens on board who didn't seem to mind the fact there was limited programming specific to them, or at least if they were bored I never saw evidence of it; maybe they were just being polite. 😃 But the shore excursions and zodiac trips were enough for them, it seemed like. Some of those shore excursions would wear out even a teenager. WiFi was good, and you can buy an unlimited package that will serve one device at a time, which for many teens is probably enough to stave off complete boredom. And we went into areas where we never saw another cruise ship. One passage we did see one other: Lindblad's opposite number, headed in the other direction on the reverse itinerary.
If it were me, and it was my 70th birthday gift to myself, I'd go Lindblad all the way and cross my fingers for great weather and lots of orcas.