Apart from external factors (elements and sun exposure), nutritional factors (dehydration, vitamin deficiency), and internal factors (hormonal imbalance), you might also want to check your actual face. It could be that your bone structure is causing your entire face to melt down, dragging down your features, making you look tired and old.
Do you still have all your teeth intact? Losing teeth weakens the foundation that supports your facial muscles and skin. This happens veeery gradually so you won't really be able to tell that that's the cause. Months or a few years later, people around you lang will start telling you you look different/tired/old/stressed even if your habits, nutrition, rest, activities are pretty much the same and you feel well naman.
Research on it: Orthotropics, Mike Mew, NCR (Neurocranial Restructuring), TMJD (Temporomandibular Joint Disorder). I'm researching on it because I lost 2 teeth from unnecessary dental extractions for my braces. This caused my face to be asymmetrical, my left side is fine, but my right side has puffier bags, deeper lines and larger pores. It's not very noticeable, but over the years (extraction was done 5 years ago) people started noticing I looked tired/stressed/sleepy all the time even when I feel well. My extraction was done on each side, but the asymmetry was caused by the uneven bite and my jaws. I used to always get mistaken to be in my teens until the extractions. Now my left side, which is fine, looks 20-ish, the right side looks 30-ish.
I have a friend who is currently being treated for TMJD. She had this symptom, she used to always look tired. A lot of people, especially Filipinos have TMJD, but not everyone gets diagnosed properly. If you look around you, I'd say 9 out of 10 people have a jaw, symmetry, structural issue of some sort. If you have this - face that looks tired all the time - and are suffering from migraines, sleep disorders, if you snore, have hormonal imbalances, and a host of other health problems, you might wanna read up on TMJD, NCR, orthotropics, etc.
