Thank you for the additional information.
The fact that you are the oldest, and were the only one terminated, may still be enough.
In order to make a successful claim for age discrimination you must first establish a prima facie case as follows:
In Fasold v. Justice, 409 F.3d 178, 184-85 (3d Cir. 2005), the court held that the plaintiff:
presented evidence that he (1) was over forty years old at the time of the adverse employment decision; (2) is qualified for the position in question; (3) suffered from an adverse employment decision; and (4) that his employer replaced him with someone sufficiently younger to permit a reasonable inference of age discrimination. See generally Potence v. Hazleton Area Sch. Dist., 357 F.3d 366, 370 (3d Cir. 2004); Anderson v. Consol. Rail Corp., 297 F.3d 242, 249 (3d Cir. 2002).
Once you are able to establish that you were subject to disparate treatment, the burden shifts to the employer to show that there was a legal reason for the adverse action taken against you.
To start the process, contact the EEOC at www.eeoc.gov for more information on filing a complaint. Your employment is protected from termination due to filing the complaint. Such termination would be retaliatory and subject your employer to further liability to you.
An attorney is not required, but it would be invaluable in this type of claim. It is not simple litigation and there is no reason you need to learn as you go. Additionally, if you prevail, you would be awarded your attorney fees and many attorneys who handle this type of claim, do so on a contingency fee basis. So, it should not cost you anything upfront.
If you need help finding local counsel, try Martindale Hubble. Many attorneys themselves use this site to locate attorneys outside their jurisdiction or expertise: