Zoom facilty in Android apps for weak eyesight
I guess I have what you need. You can use an Android application called Big Font. It lets you scale system font size from 20% [smaller] up to 1000% [bigger]. That is really a common problem when a person is aging. Time will come you will no longer be able to read small texts especially when reading it from a Smartphone unlike before.
With this Android app, you can scale up the system font size used by different apps on your phone so you can better read it on your screen. To download, visit Big Font. It requires Android 2.3.3 and higher. The latest version is Big Font 2.42. It will also allow you to preview the scaled text before you apply it so it will not be too big for your screen.