Pages compatible with my old MacBook Pro 15 inch 2011

No. The current Pages v11.0 in the Mac App Store requires macOS Catalina (10.15.7), or current macOS Big Sur (11.n). Your 2011 MBP cannot run either operating system. You can use Pages for iCloud though.

Yes, you will not be able to use Pages for iCloud without some kind of Internet connection. As for third party word or text processing alternatives that do not require a connection there are many to choose from--some free, some cost money. Here is a link to a site with some suggestions. https://www.imymac.com/mac-tips/word-processor-for-mac.html. The most often recommended alternative here on the forums (deservedly so) is LibreOffice which is cross platform, compatible with Microsoft Word and totally free.

Forgot to add one other thing. The longer you are running High Sierra on a 10 year old computer the more and more you will encounter updated software that will not install on it. Whatever text or word processing program you choose check compatibility before downloading.