You can think of "Importing" photos into Lightroom in terms of importing information about a photo rather than importing the photo itself. Lightroom can perform this importing in several ways. One is by performing a copy which will leave the image file where it is currently stored on your hard drive and another is by performing a move (called an ADD) which will move the image file from where it is currently stored into a new folder of your choosing. By default, Lightroom will create a new folder using the capture date of the photo. I do use folders as part of my management and there is really only one good technical reason to do so; if you do not tell Lightroom to perform a rename of your files during import and allow them to be stored under the name your camera assigned (Nikon uses _DSCxxxx.NEF where xxxx is a four digit sequence number), you will eventually reach a point where the camera starts reusing names as the counter wraps from 9999 back to 0001. By storing the image files in date folders, you avoid the hazard of potentially overlaying your files.
As I said, I do use folders using names like YYYYMMDD_Death_Valley. For me, this has the advantage of allowing me to find a photo on my HDD without having to bring up Lightroom. The flip side of this however is that I have been to Death Valley more than a dozen times with each folder often containing over 100 images each. Now I have to look in a bunch of different folders unless I can remember when I took that sand dunes picture I am looking for. Because of this, I pretty much never bother since I have Lightroom collections and keywords that will allow me to zoom in on what I am looking for much faster even if I include the amount of time it takes to get Lightroom started. This is where Lightroom really struts it's stuff.
After I have done my import--and yes, I still use folders--I will build any collections I think I might want/need as well as adding any keywords I want. I like collections because they allow me to group photos from many different folders in one place with a single click. They can also be nested which allows you to set up a structure or hierarchy of them. I can create a collection for Sand Dunes and one called Mosaic Canyon which are both children of the Death Valley collection. Clicking on Sand Dunes will show me only photos of Death Valley sand dunes but clicking on death Valley will show me not just photos of the sand dunes but also those taken in mosaic canyon. A collection can also be smart. This works using keyword. You can designate that this collection should include any image that you tag with a specified keyword(s) (one or more can be used). With a smart collection, if I tag an image with 'Mosaic Canyon' as a keyword, the photo is automatically included in the Mosaic Canyon as well as in the Death Vally collection because of the hierarchy I defined. Finally, you can include a photo in any number of different collections but the file still only one copy of that file on your HDD. Folders can't do this without a log of duplication of the file. If I send a batch of photos off to be printed or uploaded to the web, I will build collections for these as well so I know what I did with any of my photos.
Keywords are another level of organization that work along side of collections. As already noted, collections are a Lightroom construct but keywords are not. While it might seem redundant at first to have a collection and a keyword with the same name, it really isn't. Once you decide to copy a photo from Lightroom and send it to the web, there is no more collection but there are keywords. When you upload your photo with a solid list of keywords, your image can be found. The more keywords you add, the easier you make it for someone to find your image. As an example, if I send a sand dune image to the web, people looking for Death Valley, sand dunes, sand, dunes, desert, drought, etc. would be able to find my image (don't bother, I don't have a web site or use Facebook). In this way, keywords not only make it easy to find particular images within Lightroom but also anywhere else they may be stored external to Lightroom.
For your particular situation, looking for a photo of your son when he was 8, there are several ways to accomplish this. What I might do is set up a smart collection based on the keyword 'David'. This will gather every image you tag with 'David' into a single collection. Now that you have all of the photos you have taken of your son, you can click on the collection and now the Library mode grid display will only show you his photos. Near the top of the Library module screen is the Filter bar (the '\' key toggles the filter bar if you don't see it). If you click on 'Attribute' you can then select what attributes you want to further narrow your selection. One of those just happens to be the year the photo was captured. Click on '1996' but leave everything else set to 'All'. Once you do this, you will only see the photos you took of David in 1996. You could also do this using the Text or Metadata filters without using collections. Either method would work for you but it does mean that you will have to apply keywords to each of your 16,000+ images first. It is not a pretty task but fortunately, Lightroom allows you to apply multiple keywords to a single image, apply one or more keywords to multiple images and even to copy keywords from one image to one or more images. Start at the most granular keywords that might fit a large group of images and then redo your selection to get the next keyword that might apply. In my case, I would select all of my Death Valley photos and tag them. Next, I would select all of my images of the sand dunes and tag them. Finally, I would select all my images of Mosaic Canyon and tag them. If I have tags that might only apply to one or a few images, I will do those last. In this way, you build the organization you are looking for slowly. If used with smart collections, these will be built as you add the appropriate keywords. Good luck and happy keywording!