The short answer: No, it's not too late.
Some labs even have projects that require senior status. These labs often want students who have completed most major core requirements, have background knowledge in the lab's subject area, and have learned techniques from their instructional labs. Also, sometimes a mentor has a short-term project and can only offer a semester or two of research experience so they are open to students at any academic level.
However, in some disciplines, labs prefer first or second year students because the amount of time it takes to train a someone in safety and basic lab procedures. The main challenges you'll deal with will be finding a lab that accepts seniors or to persuade a mentor to choose you over someone who could be around longer.
If you're serious about doing a research project in a lab as a senior, though, don't put off your search any longer. Make it a priority and get started as soon as possible so you can find one (or possibly two!) positions to help you accomplish your personal and professional goals.
To help you get started on your search, read why it’s so important to Choose Your Position Wisely