This is an indication that the boss wanted to have someone he could pay less and there was no way he could have decreased your salary. This could be determined by the workload in that department because some departments require more energetic young people.
Happens all the time, it's a simple matter of $. Why pay you in your 40s $20 an hour when they can hire a kid to do the job for $10 an hour. Age discrimination is hard to prove especially if you're the only 1 getting laid off & replaced. The company simply says that you weren't performing the job satisfactorily etc.