Stay hydrated, and boost your collagen production. You can supplement with collagen powder (in smoothies and a variety of other recipes), and you can also use gelatin powder for the same purpose. Gelatin powder is cheaper than collagen, and I find it works better for me personally. It assists the growth of nails, hair, and stimulates collagen production in the skin, which all lead to a healthier, more youthful appearance.
Wear a good SPF, and make sure to get your time in the sun... 20 minutes per day, whenever the weather permits. I think it's more important (especially when under age 50) to get sun exposure than it is to begin with retinol in any form. Just like a flower, we need direct sun so that we can regenerate.
The problem with using retinol (and any vitamin A supplements) is the heightened risk of sun damage. Beginning on a renitol treatment regimen can cause an "ugly duckling" phase (acne which worsens before it gets better, lots of redness, peeling, etc.) and for some people, it can take several months to see any improvement. This can be a mentally risky approach for someone who is already feeling down about their skin. Women I've spoken to who have used prescribed retinol creams for many years have told me that they recommend a woman waits til she is a bit older (50 and beyond would be perfect), or until this type of serious treatment is the last resort. It is essentially a chemical peel that will be ongoing for as long as you use the cream.
I personally don't see fillers as a good approach, firstly because they tend to stretch the skin out, and this necessitates more and more treatments down the line when the effects wear off and the problem is perhaps worse than when it started. Just as too much weight gain can cause the skin to stretch, fillers can also cause the skin to stretch/sag. However there is a definite happy balance, as maintaining a good, healthy weight will plump the face and give a more youthful appearance.
If you wanted to take the route of cosmetic procedures, though costly, laser rejuvenation, microderm abrasion, and other such skin focused treatments are a good approach. It's all about revealing a layer of brand new skin which can then be tended to and cared for properly to sustain the 'glow' for as long as possible. The effects of these treatments can last about 5 years.
None of us stay young forever, but that doesn't mean we can't have that glowing 'new' skin... make sure you stay moisturized and exfoliated. I would recommend a Vitamin C serum. They tend to be gentle yet the effects can be profound after extended use. I call them "skin food."
Lastly, remember to be kind to yourself, in thought and in action. You are beautiful, and you are enough just as you are.