Google keeps tabs on your searches for months after you made them. Google logs every thing you search for, every email, every click. They use the information to personalize your searches based on what you have previously typed in. Google can track you across 88% of all web domains according to a recent study by University of CA, Berkeley students. In other words, there is not much you do on the internet that Google is not tracking.
If you want to see what kind of data Google knows about you, check out your Google dashboard and your account history in Google settings. If you click on “Account History” in Google Settings and scroll to the “Ads” and click to “Edit settings”, you can see what Google knows including your age bracket and what Google thinks your interests are. From here you can edit your information and manage your “Opt out” settings.
You can limit somewhat what data Google learns and tracks about you. Turn off “Web History” to start. But that alone won’t stop Google for collecting more data than you can imagine about you. The only way to stop Google completely would be to quit using the internet entirely. And we all know that’s just not going to happen.