Recently returned from a trip to Oceanside (visiting Carlsbad family).
We really enjoyed Legoland with the 7 and 9 year old grandkids. They have an annual membership and frequently go. Agree with
@Luanne, 10 or so is probably a better max age. That said, a kid into their teens could surely enjoy it (with the right attitude). I would say under 10 and the parents / grandparents would enjoy the most. We had a bad ticket experience, maybe being local you can find better deals. We had checked things out, and the desk at Oceanside had a decent deal (about $65 a ticket), but there was a computer glitch and we ended up asking for a refund (as our tickets were NOT for Legoland even though that was what we paid for). We ended up paying $90 each at the gate (because people were waiting for us and we just wanted to get there and get in). They have a fun detective twist - find Mr. Gold. Ask any employee if they have seen Mr. Gold and if they have they give you a special pin. Also look for a small bubble wrapped manilla envelope and it will have prizes? That's the scoop, we did not find Mr. Gold or the envelope, but especially the 9 year old enjoyed this 'game'. And still probably 14 too old for this. There is a waterpark I don't know anything about and an aquarium (we did not attend).
Some other really fun things we like to do in the area. Check the tides. I am now a very novice 'tidalpooler'. There were King's tide when we were there and we hit Swamis beach at low tide. Just amazing what you might find. Starfishes, octopus, etc. Lot's of people but also they were caring and careful, I don't think anyone took anything (any sea creatures). Just the thrill of finding and observing these sea creatures in their own habitat.
Looks like you don't need it to be King's Tide (although I'm sure it was helpful):
Swami's Surf Beach is a famous surfing destination at the south end of Encinitas, CA. The bluff top park at Swami's Beach has a great vantage point for
www.californiabeaches.com
We picked Swamis Beach as we also visited the meditation garden in Encitas. A very beautiful and peaceful place (but likely not of interest to a 14 year old)?
We also enjoyed the seals in La Jolla (a must do, if in the area, IMO). And the hang-gliding at the Torrey Pines Gliderport:
en.wikipedia.org
There is good food from a 'food truck' like setup. A nice set up for sitting and watching the parasailers and having lunch or a snack. TIP: Use the restroom before going there (outhouses (and not nice ones) are all that's available).
Lots of hiking around the area, too. My daughter spends as much time outdoors as possible (she has Visual Snow Syndrome) so we are always looking for outdoor options.
Last suggestion. Fisherman's Restaurant in San Clemente. It's on the pier. Awesome food, great specials during the week if seated by 6pm. Oversized servings of sherbet and ice cream. Indoor and abundant outdoor (with warmers) seating. Reasonably priced public parking close by.