Go back and read through the Dermis Post again. Just go glance at it quickly, I won't get too terribly technical with you, I promise! If you want more info, check out the reference paper below. It's a great overview of Peptides and what they have been found to do.
Ok, well, remember those cells I said were present in the dermis? The fibroblasts? Their job is to create collagen, a major component of the matrix of extracellular things in the skin. (My husband, an expert in the Extracellular Matrix is going to kill me for simplifying everything so much. His grad students would laugh at me. But, this isn't a PhD Disseration, it's a beauty blog!) One of the major problems with aging (both from age and from sun exposure) is that the skin's collagen is made is smaller amounts, what is there is broken down more quickly and the fibroblasts themselves replicate more slowly as they die off. This happens more quickly in photoaged skin than just aged skin, so the results of decreased collagen are even more pronounced.
Where do peptides come in? There is a lot of evidence that peptides can do a lot of things to help overcome this issue. Not only do peptides stimulate fibroblasts to replicate, they stimulate production of collagen and even help to inhibit it's breakdown! Peptides can even be used as couriers, bringing in beneficial things such as copper (which is very vital to wound healing, copper also helps to stabilize the collagen that is present). Now, these studies have all been done with very specific peptides, and most products don't tell you exactly which peptides are included, but there is real evidence out there that peptides work!
Reference: Lupo, MP. Cosmeceutical Peptides. Dermatol Surg. 2005;31:832-836