I started out with a very narrow palate and had a really hard time to put my tongue up there but I have been forcing myself to do it every single day for 3 years and I believe it has given results! I actually tried mewing earlier but I consider 3 years of somewhat proper mewing is accurate.
Other benefits are:
Much improved nasal breathing
Better cheekbones
Less tired
Better sleep
Better occlusion
Wider smile
Healthier gums and teeth
Cons:
It has been a real struggle to keep the posture especially in the beginning and I have become obsessed with improving my facial structure.
First pic is 3 years ago when I started at age 23 second one is from today age 26