Flying a single-seat aircraft is an experience reserved almost exclusively for pilots of tactical military aircraft--and sailplane pilots. The parallels between the two cultures are surprisingly close: both pilot communities are composed of individuals who are truly passionate about their airmanship, people who fly as if their lives depended on their being "the best of the best."
The skills involved in achieving flights of hundreds of miles without an engine will transfer across to any other flying you do. They will also unlock a world of satisfaction for you.
Tutorial: transition to gliders
In this country, the total glider-rated pilot population is split just about 50-50 between those pilots rated in gliders only, and those holding ratings in other aircraft categories. A transition pilot in this context is one who is adding a glider rating to his/her existing pilot certificate or prior flight experience. In that past, those who did were almost invariably airplane pilots learning to fly sailplanes. Nowadays there are also many ultralight pilots transitioning to sailplanes. In either case, adding a glider rating is somewhat different than initially learning to fly in gliders.
First, some similarities and advantages enjoyed by transition pilots. A rated pilot has already had exposure to the National Airspace System, to basic aerodynamics, to basic meteorology and to the Federal Aviation Regulations; this previous exposure is a good head start.
On the other hand, a pilot rated in another category will definitely have some unlearning to do! A glider flight is planned very differently; certain aerodynamic aspects of the typical sailplane are markedly different; and a more nuanced understanding of meteorology plays a much more significant role in planning and executing a flight in a sailplane. Airmanship plays a much larger role in soaring, and in fact unlike an airplane pilot, a glider pilot considers a landing as distinctly anticlimactic; after having continuously maneuvered with great precision for the past several hours, flying an elegant approach and landing may well represent a rather lightened workload--really nothing more than a simple and relaxing end to a great flight.
Perhaps the biggest difference is in the far greater significance, in soaring, of events and conditions outside of the cockpit. To a degree almost unimaginable to non-glider pilots, the art and technique of soaring both hinge on the pilot’s ability to detect subtle environmental clues. Complacency, or the willingness to idly sit by and watch the autopilot eat up the magenta line on the moving map, have no place in a glider cockpit! (It really has no place in an airplane cockpit, either, but is often found there all the same.) The successful glider pilot actively draws new information from any source whatsoever, and what would be trivial and unnoticed in a powered cockpit often reveals a key piece of information: the orientation of cloud shadows on the surface below, the detailed shape of a ridgeline, the firmness of a cumulus base, the way a growing cumulus tilts—these may all convey vital information to the soaring pilot.
This ties into one of the greatest benefits glider training offers the airplane pilot: because a glider won't wait for a pilot-in-command to make a decision, one is forced to stay well ahead of the aircraft at all times--so that even a short recreational cross-country flight represents a real workout for a pilot. A sailplane is just about the only recreational aircraft that truly requires a Captain!
On balance, a transition pilot has an advantage over an ab initio student, but that advantage is probably a good deal smaller than one might think. Glider instruction has as much to offer a rated pilot as to an absolute beginner.
How about the FAA requirements for transition pilots? For starters, the certificated pilot adding a glider rating need not take the knowledge test; he or she is presumed by the FAA to already know most of the material covered in the written exam. (Expect to be quizzed on your understanding of these topics by your designated pilot examiner, of course, as well as on those topics unique to gliding.)
As you might expect, FAR 61 flight time requirements for transition pilots are rather modest: while there’s a little fine print in the regulations, the take-away numbers are three hours of dual flight time and 10 solo flights (for a Private rating) or 20 solo flights (for a Commercial rating.)