Can you please tell me how long the statute of limitations is for "failure to appear" in the state of Maryland?

Failure to appear at what? If its failure to appear at your triial, then SOL doesn't apply. Failure to appear usually means a bench warrant which doesn't expire.

A statue of limitation is the time from when a crime happens, to when the person is charged.

So on a failure to appear you are normally charged the day it happens.