What visa options are available for long-term stays in Thailand under 50 years of age?

Honestly the best thing is to bounce around SEA. If you decide to stay here long term when you turn 50 you will be clean on your passport.

If you arrive before April 1st without a visa, you'll be stamped in for 45 days, and you can extend one time for 30 days.

You can see if your embassy will sell you a multi-entry tourist visa. This is valid for 6 months from the day it is issued, and each time you enter the country in those 6 months you will be stamped in for 60 days, which you can extend for 30 days.

This means if you enter and do 60+30, then leave and return for 60+30, then do that one last time just before the visa expires you can get a final 60+30 and get almost 9 months out of this visa.

Many embassies now require you to prove the need for a multi-entry tourist visa, which usually includes proof of a flight to Thailand, proof of booked travel out of Thailand within 60 days, and then proof of another flight returning to Thailand after that. If they are not satisfied that you need the multi-entry visa they will just give you a single-entry but keep the extra that you paid for the multi-entry.

An education visa may be a viable option for a year after your initial arrival. Beware that there was just a large investigation into ED visas, so expect to have to attend class and make progress in learning Thai, as you will be asked questions in Thai when you go for your 90 day extensions (the ED is only given 90 days at a time).

After that your option are very limited. Elite visa as you said. Get a job in Thailand and a non-B visa. Get married and get a Thai spouse visa. Have a Thai child and a visa based on that. Staying long term without a long-term visa is no longer an option.