Whenever you start noticing fine lines, less firmness, or dryness that won't let up. A lot of people begin in their late 20s or early 30s as a preventive step, but there's no fixed age. Your skin will tell you before a calendar does.

Serum goes first. It carries the concentrated actives that do the targeted work, and the cream comes after to seal moisture in and support the barrier.

Yes, they're usually used at different times anyway. Vitamin C serum tends to go on in the morning under moisturizer, and the anti wrinkle cream fits into the evening routine. If your skin is sensitive, bring in new actives one at a time rather than all together.