When the thermals stop working, the glider will gradually descend. A glider can fly about 10 km for each 1000 feet of height, so there is a good chance that an airfield will be within reach. In the event of no airfield being within reach, the glider will land in a paddock. Paddock landings are part of the training of every glider pilot once they are ready to fly cross country. The glider can be retrieved by a tug, or, of this is not possible, the glider is disassembled and returned to the airfield in its container.
Gliders can remain flying as long as there is lift available.
Using thermals, this is about 8 hours. By using prevailing winds blowing up a slope, a glider can be flown for as long as the wind is blowing. The world record stood at around 56 hours before it was recognised that these ever lengthening flights were dangerous, and recognition for duration flights abolished. The lower age limit to fly solo is fifteen, and there is no upper limit provided you are healthy, and suffer no medical conditions that may impede your ability to fly. To be a passenger in a glider you can be almost any age at all.