What type of visa should I apply for to stay in Thailand for three months and later transition to a retirement visa?

If doing 90 day stints, maybe a tourist visa is better to start? You can get the drivers license quiet easily in that first trip if you'd like or use an IDP from home until then.

I'd go for a tourist visa this and next year, 60 days plus extendable another 30 days. Serves your 90 day purpose of tourism.

Visit for 90 days: OR the Non Immigrant O visa based on being over 50 years of age, which gives you 90 days on entry.

OR the Single Entry Tourist Visa which gives you 60 days on entry and can be extended once with 30 days on basis of tourism.

In 2024 a long way ahead, but the retirement visa also know as the Non Immigrant O visa based on being over 50 years of age from the Thai Embassy and when arrived in Thailand apply for the 1 year retirement visa also know as an Extension of Stay based on being over 50 years of age at the local Immigration Office.