Q&A for How to Start a Wiki

You can use TiddlyWiki, which is a free and open source personal wiki that I've had good experiences using. It can be used as a personal web notebook. You can download empty .html files from their website and edit or create new tiddlys (wikis) to save. Your browser automatically downloads a new html file with any changes.

Age does not matter as much as effective leadership. In other words, yes you can, but be prepared for the huge responsibilities that follow!

Yes. You would need a self-hosting wiki where you can restrict access. Try Wordpress wikis. My favorite is Helpie wiki. See Helpie WP in an internet search. You can restrict access by giving login or you can assign specific user roles to each user.

Yes, you can! The best software to do this is MediaWiki, the software that runs WikiHow and Wikipedia. You can protect articles so that only good users or admins can edit a page. MediaWiki also has an option during installation that you can make your wiki as "Authorized Editors Only".

You can click the “Edit” button next to the pencil and change the things you want. Click Save, and voila!

You can use Google Adsense to generate revenue with advertisements.

While you can still use normal web hosts, I suggest that you host it on a spare computer you own. If you don't have one, you can buy a $25 Raspberry Pi Model A to host it from. See raspberrypi.org for more information.