I was recently laid off from a company. They paid a severance and I signed a release and separation agreement. Can I sue on grounds of age?

I was laid off from a company and it was due to what they say was company restructure. There were several of us that were laid off in our Region and paid a severance in return I signed a release and separation agreement. I now understand that those who were let go for the most part were older long term employees and I truly feel that I was let go due to age discrimination. I was told that they took job performance into account when evaluating who would be let go. I have never had a negative review nor have I ever had any written coachings after 8 years of employment. There are other discriminatory factors that may have also came into play as well. I would just like to know if I can sue them based on Age Discrimination?