Where can I find a book with a specific type of protaganist?
Try searching on GoodReads. This site has a lot of member-created lists which you can search directly. GoodReads's Listopia can be found here: https://www.goodreads.com/list
For example, if you are looking for an elderly protagonist, try searching for "elderly characters" or "elderly protagonists". This brings back several lists for you to explore. Click on individual book titles for descriptions and reviews.
If you find a title that the High Library doesn't own, you may request it on interlibrary loan.