i'll first say that i'm 33 and am an experienced guitarist - i'm also a good chord chart reader and alright rhythm chart reader. i bought three books all at the same time to help me with my sheet music reading insecurities: Guitar Fretboard Workbook by Barrett Tagliarino, Guitar Reading Workbook by Barrett Tagliarino and this one. And actually I lucked out! Each of them progressively lead you into the next (sort of). The Guitar Fretboard Workbook was good for identifying note names on the fretboard, then the Guitar Reading Workbook was more of a beginner's guide to the world of reading music (for the guitarist), lastly this one give's you the more in-depth exercises without going overboard too fast. I know some music theory/reading books start off at a slow pace in the first 5 pages then slam with you with things above and beyond what you even want to learn. I would recommend this book as it starts off easy for beginners and moves slowly forward with good exercises and "real" musical excerpts/arrangements to play.
For guitar I see reading music split into two different disciplines: Knowing to read the notes on the staff, and knowing where the notes are on the strings of the guitar. My point is, on say the piano, there's only one key on the keyboard that'll play the note you're looking at on the sheet music, while on the guitar you could possibly have 4 different options to play the same note (of course you'd have to take into consideration the technical feasibility of playing the note). So, as someone who's *very* proficient playing guitar (20 years in fact), I'd recommend even to get a supplementary book like the Guitar Fretboard Workbook to help you with being able to identify where the notes are on the strings, and this book here to help you put the two disciplines together.
Hope this helps!