Font size.

There is an app in the Google Play Store called Big Font. The link below is to the free/eval version, I do not know how much the Pro version is.

https://play.google.com/store/apps/details?id=com.a0soft.gphone.bfont

This can scale the fonts up to 1000% (10x), including system menus.

HOWEVER, it will only scale fonts that were written/coded as scaleable, so applications written with hard-coded font size will not be affected.

As for the Notification Area, there is an app in the Google Play Store called "BIG Notifications". Apparently you can set the font sizes for the system notifications and also zoom them. Here is the link:

https://play.google.com/store/apps/details?id=cz.twobig.notifications

This also has a paid version but I do not know the price.

Both of these have a free or limited version which should tell you if the app is going to work as you'd like or not; although some may have limitations in the free versions. Good luck and let us know if either of these are suitable.

Oh, I forgot to answer the part about the text beneath the desktop icons. You can somewhat have control over this by using a 3rd party launcher application. While I am not so sure about changing the actual font size of the text underneath the icons (most launchers allow this but there is a limit to the size, as the majority of users don't need super large fonts) -- you can change the grid size. That is, your icons might currently be on a "5 wide" grid, meaning 5 icons left to right. You can change the grid size to be "4 wide" or "3 wide", which makes the icon larger and MAY allow the text to be larger. However, I doubt that, and I would guess that it may only allow more text to be visible rather than larger text.

So there might not be a good way to get large text on the launcher (home screens) but with a 3-wide grid, the icons themselves may be large enough to recognize without the need for any text. Many launchers have the option to not show the icon text at all, so rather than chopped off text or funky looking text that is so large you can only show 4 characters; you can download free "icon packs" for your launcher that let you customize each icon. So you can set the Phone app to a "big green telephone-lookin' icon" and it'd be hard to mistake for anything else (no insult intended, just meant to illustrate that maybe you don't need the text for your desktop icons).

Launchers are varied and many in the Play Store. Personally, I use Nova [Prime] but there are many out there that should do what I described above. Nova does let you set the grid size -- Edit: just looked and Nova only goes to 4 wide. There are some "big button" launchers out there too, but I haven't read too much about these. Here is one called Big Launcher, which seems to go 2-wide but I think icon text is not an option there but at that size, hopefully you will not need it.

https://play.google.com/store/apps/details?id=name.kunes.android.launcher.activity