It's not a 7 day "extension". Technically they deny your extension and give you 7 days to leave the country. There is no such thing as paying to overstay when you have been ordered to leave.
At age 50 you can apply for a retirement visa. Consult a visa agent as soon as you land in Thailand to get everything set up before your birthday. I was able to switch from a visa waiver to the retirement visa without even leaving the country.