You could try
Match.com or
eHarmony as they are geared more to people in their mid 30's and 40's. You must be a paid member to communicate though.
POF is a free service that you can try that is also popular with people in our age group (I am in my 40's as well). They also offer an upgrade which removes ads and gives you a few more premium perks. The "free" dating apps all have a paid upgrade option and they tend to have more "fake" profiles since it is easier to message people.
Another good option is
Bumble where women are the ones who must communicate first.
I hope that helps.