Layering is where routines fail, and almost always for one of two reasons: the order was wrong, or a layer had not set before the next one went on. Both are free to fix, and neither is a product problem.
The order follows one principle — thinnest and most absorbent first, most film-forming last — with one chemistry rule overlaid: water-based products go under silicone-based ones, never the reverse. Silicone is hydrophobic, so water does not spread evenly on it; a water-based product applied over a silicone film beads up and the two layers roll together into the little grains people call pilling.
The waits exist because every layer needs to reach a stable state before the next arrives. A wet layer plus a wet layer equals a mixture, and a mixture shears under your fingers or a sponge. Two minutes after moisturizer, a minute after sunscreen, a minute after primer — about four minutes of waiting across a whole routine, and it eliminates most pilling.
One more principle specific to mature skin: the fewer layers the better. Every film on a face that creases is another thing to crack along a fold, so the correct routine is the shortest one that solves the problems you actually have. Several of the steps below are optional and most people should skip at least two.