I've been doing this for years, much to my enjoyment. Simply ask the girl concerned. Make sure you, especially your hands, are clean, nails cut and no sharp edges. Ask if she wants a light touch and dry or a heavier massage with oil. As you go, ask if what you're doing is ok. Don't just grab and grope, if you want finger play again ask. As some parts of me don't work as they used to I find so much enjoyment in touching, now a days a booking, either escort or massage, involves about 45 minutes of massage (on her) and finishing with sex. Just ask