in that case you can leave and re-enter as many times as you want up to next May as long as you get a re-entry permit from Immigration before you leave. You can get a Single or a Multiple depending on your plans. You need to make sure you are in Thailand next May for the next annual extension.
FYI the 90 day visits to immigration have nothing to do with your visa or staying in the country. It’s just a requirement for all foreigners to report their address to immigration every 90 days, even if they haven’t changed address.
When you leave the country the 90 days re-sets so you’ll have to report 3 months after your arrival.
You should also report within 24 hours of getting back to Thailand (though some immigration offices tell you it’s not needed)
it is now available for over 50. I applied for the single entry recently and had the option of the multiple. I know someone that was issued the multiple yesterday.
The current page on the website shows both the fees and the visa types: