Pitchers in their middle-20s tend to add a little velocity, some from adding strength (which peaks in the late 20s for most athletes), some from refining mechanics. The operative word is "little", like 1-2 MPH. ranger added about 1 MPH in his mid-20s
Sanchez has actually gone from 93.9 (SSS) to 93.2 to 92.0, probably b/c they want him to focus on command rather than throwing as hard as he can - so as he gets more comfortable, an uptick the next couple years is a real possibility. His improvement this season is in his slider, had a plus changeup but the slider is now another plus offspeed pitch.