Since the YouTube app no longer works or is compatible with your 8-year old iPad, you can use the YouTube Website in a Web browser.
Speaking of Web browsers,
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 and 10
Available and better known, more popular third party Web browser choices are GONE, now.
There are still a handful of iOS 10 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
Pick two that have had the most recent of app updates.
BTW and FYI,
These 8 and 9-year old iPad models will be soon rendered fully obsolete by the end of 2020!
Here's why and what you will need to do about it in 2020!
Tap and read my link below for my additional info about your old iPad model.
If you own OLD 8 and 9 Year Old iPad mo… - Apple Community
Sorry & Best of Luck to You!