And unless you were to ask the guys/gals that are staring at you/your gal pal just what they are actually thinking, all you can really do is "surmise".
If you think about it logically (and that may not be actually happeing here), if you are with your 21 yo daughter and nobody thinks anything about that, how can you really think that if you are with a 25, 35 45 yo provider that anyone would really think that she is a paid companion?
I have been out with some very nice looking gals at public places, but the gals always dress appropriately. And I can also feel those "eyes" checking her out (maybe they're checking me out...but I doubt it). But also when I have gone out with my 25 yo daughter (who I think is absolutely adorable...but I am the Dad and that is what we think), I see similar eyes checking her out. But I have never really considered that these guys/gals are thinking anything other than "what a lucky guy to be with that gorgeous gal".
Or maybe that is just how I care to rationalize that to myself.