She looks younger because the ref above is younger :). But now you have a good base to make adjustments from. What I would look at is the eyelashes on the outer part of the eyes, they should follow the contour of the eye the line youre creating should be done with make up.
Just aesthetically i would make her lower lip fuller than her upper lip how you do that is up to you. You can lower to top lip or you can lower the lower lip .
I would also lower the top eyelids or maybe the whole eyesocket. This should give her a more neutral expression. Remember, your reff is smiling. Maybe lower the eyebrows a bit too.
If you want to make her look older sharpen the creases under the eyes and next to the nose. and make the cheeks a little less puffy maybe. Basically you want to hint at the bony forms just a tiny bit.
The neck muscles could be smoothed out a bit even for 25 they are too strong. and their angle should be a bit wider they attach behind the jaw.
Also just as a side note google some makeup for the eyes and such. No female model is complete with out a litte makeup eye liner a little eyeshadow. It can be subtle makeup but i think a little eyeshadow would help.
Another thing, for the eyebrows go with lower particle count and raise the length of the hairs. You may have to manually plant the hairs in some places to get the shape you want. And then comb them into shape(this will be a pain.) You will get more realistic eyebrows this way. You can use one or two children for those hairs with a little clump.
Have you considered giving her glasses? I think it would suit her. Something with a square black frame.