Employees need more than a hunch that their employer discriminates based on age. They need some kind of proof.
Employers who can document that they had a legitimate reason for disciplining or firing an older worker will usually win the case. That's why your records should clearly show why you did what you did.
That way, if the employee sues, you'll meet your initial burden of proving that you had a legitimate reason for termination. Then, it's up to the employee to counter with proof that your stated reason was just an excuse for discrimination. That's hard to do when all the employee has is a vague suspicion.
Recent case: Oscar Garza, age 51, worked for Claymex Brick and Tile as a warehouseman. The company required him to conduct a monthly inventory of the materials by the first of each month. When he failed to do that one month, he argued with his supervisor about the reason. The next day, the supervisor fired Garza for insubordination.
Garza sued for age discrimination under the Texas Labor Code. A jury found Claymex was motivated by age when it fired Garza. But on appeal, the court tossed out the jury award, concluding that Garza had no evidence to put Claymex's reason into question. Garza cited nothing more than his suspicions of discrimination. That's not enough. (Claymex Brick and Tile, Inc. v. Garza, No. 04-05-00433-CV, Texas Court of Appeals, 2006)
Final tip: Don't be afraid to enforce reasonable civility rules. Just make sure you do so evenly. Don't let certain employees skirt the rules; that could be viewed as evidence you used the rule violation as a convenient excuse.