Regardless of whether you're getting your information online or offline, the publication date will play a role in its validity. Some subjects will never change over time. You can easily look up information regarding historical events or the arts and see factual information even in older books and websites. When you look for information in areas that are evolving, such as science, be sure to check the date your source material was published to determine if you need to find more current data.
The library houses many ways for you to validate information. A quick talk with the librarian will lead you directly to the resources you need. You can use library databases as well as a number of indexes and periodicals. There are also a variety of reference books that house factual information. Depending on the subject, there may be a reference book designed strictly for that area of expertise. Spend some time going over every resource the library has to validate the information you're questioning.
Very little information is written from first-hand experience. This means that every author acquired it from a source. As you review information you know isn't first-hand knowledge, look for its sources. Not all authors list their sources; when they don't, that might be a red flag, and when they do, it gives you the opportunity to validate it, as questionable sources are another red flag.
Anyone can produce information, but that doesn't make them reputable. Always take the time to find out about the credentials of the author of any information you want to validate. Oftentimes, the person who's writing about a particular subject has the education and life experience to make them somewhat of an expert in the field, something that increases the validity of what they have to say.