How di I find out the max mb speed in older airport extreme

There are 10+ versions of the AirPort Extreme, so it is difficult to know which "old" model you might be referring to.

If by "old", you mean that you have the "round" or "dome" shaped version of the AirPort Extreme, the maximum wireless speed that you will attain is about 50 Mbps. IF you will be connecting a device to the Ethernet port on the AirPort, then speeds up to 100 Mbps can be attained.

If by "old" you mean that you have a "square" or "flat" version of the AirPort Extreme, we need the model number (on the bottom of the AirPort.....starts with an "A" followed by four numbers) to be able to provide an accurate answer to your question.

Almost all versions of the A1143 can handle up to Gigabit (1,000 Mbps Link Speed, typically about 500 Mbps actual) Ethernet speeds and typically about 300-500 Mbps over wireless.

If your Internet connection speed is 90 Mbps, then the AirPort Extreme will of course be limited to 90 Mbps on Internet connections for both Ethernet and wireless.

To make things confusing, there were a very limited number of 1st Generation A1443 sold. Those models had 10/100 Mbps Ethernet ports.

AirPort Utility on your Mac will tell you whether you have a 1st Gen or 2nd Gen version of the A1143. Most likely, you have the 2nd Gen.

You've the 2nd generation Airport Extreme

It could also be the first generation with the same model number.

The difference is that the 1st generation has: