If I am praying next to an elderly person who I know is somewhat dependant on my help to find the place in the prayer book, at what points in davening may I silently direct him to the correct page/place (eg by turning the page in his siddur or pointing to where the chazzan is up to)? Can this be done while I am still saying shmona esrei if the chazzan begins his repetition before I am finished?  I expect I can at most if not all other points in davening, but am open to hearing otherwise.  Does it matter if someone else might come over to help if I don't?  

Partially inspired by: http://judaism.stackexchange.com/questions/40187/am-i-allowed-to-interrupt-someone-in-the-middle-of-shmoneh-esreh-if-my-question though in my case the help is going the other way.