There is so much you can do here in SD, depends on what you want to do and where you are staying…
On the bike, suggest hooking up with a bike club for a Sat ride,
One of my favorite longer training rides is from PT Loma light house to the east end of San Luis Rey bike trail will be 80 plus miles, or hill repeats inside Torrey Pines,or hill repeats on Soladad , dont ride much in east county as drivers not as friendly but some major freaking climbs… Fiesta Island is a great place to put the hurt down… is a one way road that has a short loop and a long loop, they have TT races there every couple months( google Fiesta Island TT) … or bring your state issue ID and you can ride through Camp Pendleton up to San Clemente, couple nice hills , good TT bike course, and You gotta do Sleeping Indian up in Fallbrook, oh what fun…!
Runs… your brother would like Cowels Mtn trail run/hike, 6 miles round trip great training run or nearby Mission trails (get a trail map from the visitors center), both take water… Iron Mtn Rose Canyon Tecolote Canyon,(if warm there can be snakes… Mission trails has the biggest Rattle Snakes I’ve seen), not a fan of Mission Bay as alot of cement sidewalks , ALTHOUGH the 2 legged sites are pretty dang good , La Jolla Cove a good place to run for the sites too, watch the road/ sidewalk as alot of tourist and holes cracks, good run is from the cove to PB and back… 13 miles some water , bring your own… My Favorite is Carlsbad train station south down to Leucadia (South Puntos state beach… do the stairs behind the bathroom refill water at the bathroom head north) and back along the coast, 13 plus miles water available a few places, vey pretty run…
Hiking…I like my peak to peak in Cuyumaca State Park… Cuyumaca peak to Stonewall Peak back to the car (9 miles I think… at 4,000 plus feet,) down to Julian , grab an Julian apple pie maybe eat at the Julian Inn head home, plenty of trails off of Sunrise highway
Mtn Biking… Mission Trails… Daily Ranch (decent hills) Rose Canyon dont stop and look around or you might get a date … I dont do much mtn biking anymore … although Alpine has a epic trail dont rememebr then name
Find a female friend , Gaslamp or any spot around San Diego State ( La Jolla for happy hour),Del Mar is kinda poser wine drinkers, Carlsbad has alot of cougars out trolling ( West Bistro and Coyote Grill)
or if you are a rainbow guy Hillcrest just wear your tight fitting clothes.
I am not a fan of TJ … not my scene and a little sketchy … not sure how much of the under 21 crowd goes there anymore