Dragons will have the Wild Animal meta-trait, minus the fixed IQ taboo trait. So they have Bestial [-10], Cannot Speak (Cannot Speak) [-15], and Hidebound [-5]. They also have the Quadruped meta-trait, which has Extra Legs (Four Legs) , Horizontal [-10], and No Fine Manipulators (No Fine Manipulators) [-30].
Young Adult Dragon (50 years old)
ST: 20  DX: 14  IQ: 5 [-100] HT: 14 
HP: 20  Will: 10  Per: 12  FP: 14 
Basic Lift: 80 lbs. Thrust: 2d-1 Swing: 3d+2
Basic Speed: 7  Basic Move: 7 
Dodge: 10 Parry: 0 Block: 0 SM: +1 (9')
Traits: Affliction 1: Venom (Moderate Pain, +20%; Follow-Up: Teeth, +0%) , Ambidexterity , Claws (Talons) , Cold Blooded (Below 50°) [-5], Damage Resistance 6 (Cannot Wear Armor, -40%) , Discriminatory Smell , Extra Attack 2 (Brawling Skill Only, -20%) , High Pain Threshold , Innate Attack: Acidy Spit (2d Corrosion) , Nictitating Membrane 2 , Night Vision 9 , Quadruped [-35], Resistant (Occasional: Disease; Immunity, x1) , Resistant (Common: Poison; Immunity, x1) , Striker (Tail; Crushing; Limited Arc: Behind, -40%; Reach: 1, +100%; Clumsy: -1, -20%) , Teeth (Teeth) , Unaging . Wild Animal [-30]
Skills: Brawling (DX+0/E) - 14 , Innate Attack (Projectile, DX+0/E) - 16 , Stealth (DX-1/A) - 13 
So there we go. That's your average young dragon, a 9 foot long lizard. The venom causes the irritating effect moderate pain, which penalizes skill and attribute rolls. It's got a tail it can hit folks with, and some teeth and claws, along with the acidy spit. It's only 249 points, so it's probably fairly easy for a group of three 250+ point characters to defeat, but it's not something to scoff at. This guy has a minimum of 3 attacks per second. If he doesn't want to have any active defenses when attacked, he can make one attack maneuver an all-out attack and turn that into 4 attacks per round. His claws are going to deal 1 - 11 damage, and if that gets through damage resistance, it's cutting or impaling damage so it will have a multiplier of x1.5 or x2. The bite is only going to deal 0 - 10 cutting but if it gets through damage resistance, it has the venom attached to it too. If if feels like its prey is t0o armored to hurt, it can back up and spit acid at them. But again, this is a young guy and adventurers have been unimpressed with baby dragons since the seventies. In most fantasy stuff, dragons just keep getting tougher and tougher the older they get. So do these guys. I'm going to stick with the concept of age categories from Pathfinder/DnD, because I like them.
So at each age category, this guy is going to improve in capabilities, so I'll add this stuff to the template:
Age Category Improvement: Young Adult to Adult
Traits: SM +2 (15') ST +2 (cost factors in adjustments for increase SM) [-2], HT +1 , Affliction: Venom 2 , Damage Resistance +3 (Can't Wear Armor, -40%) , Innate Attack: Acidy Spit (3d damage) , Nictitating Membrane +1 , Skill Increases (DX+1/DX+1/DX+0) 
Age Category Improvement: Adult to Mature
Traits: SM +3 (21'), ST +3 (cost factors in adjustments for increase SM) [-3], HT +1 , Damage Resistance +4 (Can't Wear Armor, -40%) , Innate Attack: Acidy Spit (4d corrosion damage) 
Age Category Improvement: Mature to Old
Traits: SM +4 (30'), ST +3 (cost factors in adjustments for increase SM) [-9], HT +1 , Damage Resistance +4 (Can't Wear Armor, -40%) , Innate Attack: Acidy Spit (4d corrosion damage) , Nictitating Membrane +2 , Skill Increases (DX+2/DX+2/DX+1) 
Age Category Improvement: Mature to Old
Traits: SM +5 (45'), ST +3 (cost factors in adjustments for increase SM) , HT +1 , Affliction 3: Venom , Damage Resistance +4 (Can't Wear Armor, -40%) , Nictitating Membrane +2 
One note, you'll see that as we increase the the ST, there's a negative points value. This is because due to SM and No Fine Manipulators there is a 50% reduction in the cost of ST. No Fine Manipulators shave's of 40% of the cost of ST and each SM shaves off another 10%. This is to compensate for the fact that every SM increases makes the character/creature easier to hit. So an old dragon is attacked with a +5 to skill. After SM gets to +4, and we hit an 80% cost reduction for ST we suddenly jump up in costs for ST increases. You cannot get a cost reduction bigger than 80% on anything in GURPS, regardless of modifiers. There's no cap on how much you can increase a cost by though.
So by the time we increase the points of the dragon by 63% (to 386, still well below three 250+ point adventurers) we've got a creature with a DR of 21, a bite that does 3d-2 cutting damage with a venom that is resisted at HT-3, a tail that does 3d+1 crushing, claws that do 3d-1, spit that does 4d corrosion damage, that has at least 27 hit points, a basic speed and move of 8, and a base dodge of 11. Oh. And it still has three or four attacks per round. I'd probably increase the potency of the venom at ancient age, along with increasing the ST bonus per age category to +4 and the damage resistance to +5. I'd also probably pepper a few IQ increases in there as well, just for shits and giggles.
I'd also create template variations for the variations of dragons found in Hekinoe. Ambush dragons would start out with a higher DX and lower ST and increase ST and SM at a slower rate. Bestial dragons would start out with a higher ST and HT and have the Berserk disadvantage. Brood Dragons would have some Injury Tolerance, increased initial Damage Resistance, along with Allies with the Summonable enhancement. Hehehehe. Cave dragons would have an in initial SM of 0 and increase at a slower pace, but would also have a tunneling ability and Camouflage with an Environmental modifier, probably a higher initial Damage Resistance as well. Clacker dragons would have Striking ST on their bite and their Innate Attack would be split between burning and corrosion damage, or I might just add incendiary to it as a damage modifier. Some types of clacker dragons also fly/flew (the surface types are mostly extinct) so they'd have Flight. Crystal dragons would have Resistant to psionic attacks, probably upgraded to Static at higher age categories, along with Camouflage with an Environmental limitation. Fell dragons would get Magic Resistance, remain at SM +1 and probably have a higher initial IQ. The Nel dragon would have Static (Gifts; Resistable) and its venom would have the Cosmic enhancement so it could affect Nel.
Dragons. Now where did I put those dungeons?
Edit After the Fact: Based on data from a post that will appear Wednesday, and some slightly realistic considerations, I'm modifying dragons. Their Damage Resistance will now have the Semi-Ablative modifier for -20%. This reduces their base template by 6 points and the age category templates by 3, 4, 4, and 4 character points. I intend to represent all Damage Resistance that stems from bone or scales or shells or chitin or whatever with this modifier in my campaign world.