Is there any specially published reading materials for the elderly readers? such as books/magazines with larger letters or font so that they can read easily.

There are some large print editions of books. You can check their availability in Helmet by using search words such as "large print" or isotekst*.

Here are the search results:
http://haku.helmet.fi/iii/encore/search/C__S%28isotekst*%29%20f%3A1__Or…

http://haku.helmet.fi/iii/encore/search/C__S%28%22large%20print%22%29__…

There only seems to be one magazine in large print in Helmet libraries:
http://haku.helmet.fi/iii/encore/search/C__S%28isotekst*%29%20c%3A1__Or…

If you are also looking for materials the contents of which are aimed at elderly readers, there are books like that too. One typical example this kind of books are the handbooks of using computers and the internet, written especially for senior citizens, e.g. the following:
http://haku.helmet.fi/iii/encore/search/C__Sseniorin%20tietokoneopas__O…

For more information, please consult your nearest library.