Is it enough to just wash your face with lukewarm water twice a day, or do you have to use face wash/gel/scrub?

Depends. Depends upon your individual skin/ its possible problems. dryness vs oily, any acne?? If you are healthy your age suggests that you should expect good looking skin! Ask question with more info!! Dr Z.
Skin care. Depends on what you want out of washing your face. Natural oils serve to protect our skin, keep bacteria from infecting us, and generally protect us from the elements (cold, wind, rain, etc). Sometimes people overproduce and need to reduce skin oils, so they need to use soaps. If you go that route, mild is best - cetaphil, hypoallergenic soaps, etc. Gentle wash with water is good otherwise.
Well,.... A good soap along with luke warm water would be best for general cleaning.