If you like a laid-back atmosphere that's safe and friendly, drive down to Sayulita, located about 35 miles north of Puerto Vallarta. It's a village of about 4,000 souls, and it plays host to folks who appreciate good surfing, excellent fishing, abundant and flavorful food (muy sabroso), and endless summer sun. There is a curated website (sayulitalife.com) that provides reams of really helpful and accurate information about activities and lodging (there are plenty of casita rentals available at favorable exchange rates). If you fly in, choose the airport at Puerto Vallarta (and take an official taxi, not a gypsy cab - it's about a 45 minute drive). English is widely spoken in both Puerto Vallarta and Sayulita, at least enough for an English speaker to get by without problems, although the more Spanish you can speak, the more rewarding your experience will be. The singles who travel there are mostly 20-30-ish. There are a number of really, really popular watering holes, so meeting folks after nightfall isn't a problem. The town is completely walkable, and has a colonial vibe. It's not as developed as Cabo San Lucas or any of the "major" spring break destinations, but it has more charm and a much more relaxed pace. More than a few Americans and Canadians return regularly. Summer temperatures are hot, regularly recording temps in the mid-90's. High temps in winter are usually in the upper 70's, and evening breezes off the Pacific are blissful. If you can afford it, a casita rental with a view of the Pacific will deliver the best possible experience, and the best ocean breezes.
Finally, always, always insist on bottled water. (This last bit of advice is from the best authority.)