The YouTube app is no longer available nor supported on iOS devices running iOS 9 and earlier.
You may stiil be able to access the YouTube Website through a Web browser.
I would STOP using that nearly 3-year old Safari web browser, as it is, probably, not safe and secure to use any longer, and seek out a third party web browser that is STILL currently being updated and STILL being supported on iOS 9.3.5.
Here are a few third party web browsers that I know are STILL being updated and supported on iOS 9.
Available and more popular third party Web browser choices are dwindling faster, now.
There are still a handful of iOS 9 and earlier supported third party Web browsers.
Most of these have had recent updates, too!
Here’s what’s left.
iCab Mobile Web browser
Aloha Web browser
ALook Web browwer
Dolphin Web browser
DuckDuckGo Private Web browser
Snow Bunny Web browser
Maxthon Web browser
Private Browsing Web browser by Savvy Soda
Private Browser Deluxe
TOR browser anonymous
Turbo VPN browser
TOR + VPN web browser private
Good Luck to You!