Hi guys,

I'm looking for a little bit of assistance with an encounter I want to run in a few weeks time.

I currently run a session for 4 players who are all level 5 and will probably be level 6 by the time I run this encounter.

I'm wanting to pit the party against their first dragon but looking at the states it seems that a young dragon is a little underpowered and won't push the party but then an adult dragon would outright murder them.

I would ideally like the encounter to be challenging with a little risk of death but not completely deadly.

I'm thinking if I give a young dragon a little buff or an adult dragon a little nerf that should be sufficient but does anyone have any questions on how I should go about doing this?

Thanks in advance for your help. :)

give each dragon spellcasting ability. I dont get 5e and not doing that to begin with.

So give the young dragon spellcasting? That could work...

Yes. In 3.5 dragons often carried potions or magic wands to aid them. At the start they'd spend 2-3 rounds chugging Bull Strength, Haste and such. That's why I rather simplify it with some spellcasting ability. Every dragon should at least have some of it, even if its only low level spells here and there.

Also think about environment. How long has your dragon been in the area. What is it up to? Its presence would have altered the environment. Allowing you to add some environmental and other thematic stuff along the way to soften up your party...before they even get to the main fight.

I might be wrong (or your party might be a wandering collection of powerful magic items already), but a Young Dragon with CR 10 (5,900 XP) against a party of 4 level 6 character would be considered a Deadly encounter according to the DGM.

Remember that tactics go a long way towards really making an enemy dangerous, but even at its most basic a Young Dragon does 3 attacks at +10 to hit, giving it a pretty good chance of hitting even an AC 20 adventurer, dealing 17-13 damage with each for a total of most probably a dead Wizard/Sorcerer every two turns.
Also unless your whole party has flight or ranged capabilities, the dragon can retreat in the air and shower them with its breath every so often until they are softened up/charred to the bone.
It has "only" 18 AC, but 178 HP, so unless your characters are able to collectively hit and dish out 50+ damage every turn, the fight is unlikely to end with all yours still standing, imho.

I personally like Kobold Fight Club.  They can help you build encounters based on party size and level.  A young red dragon is a CR 10 which is a deadly encounter, but a young white dragon is a CR 6 which is an easy encounter.  A young blue dragon is a CR 9 and a young green dragon is a CR 8 both of which are hard encounters according to Kobold Fight Club.  If you want to use it here is the link:  http://kobold.club/fight/#/encounter-builder  

This is only a suggestion but it's still a good resource to have for the future.

Yup. I agree with WeldingBear. You shouldn't need to nerf or buff anything, just pick the right dragon.

2 sessions back I ran a Young Dragon vs. a party of level 5's, and they barely made it out of that one. It WAS in lair, which admittedly does bump its strength up a bit, but a Young Gold Dragon is a higher CR, and should be a reasonably difficult challenge for a level-5 party, if not a potentially lethal one.

If you want some ideas on how to potentially increase the difficulty, consider using a higher amount of health for the dragon. Rather than using the average health, you could look at the dice used for its health, and then use the maximum, or an amount closer to the maximum. You can also use 4 or 5 turns for getting its breath attack back instead of 6. These are pretty simple, small ways to beef up an encounter with very little effort or preparation required. 

You could also use spells or terrain. Terrain is pretty self explanatory- if the dragon grapples a PC and throws it off a cliff.... they aren't in for a fun time. The dragon could also duck behind a hillside, house, etc. for cover, fly upwards out of melee range after its turn to mitigate the damage of melee fighters or wait for its breath attack to recharge, etc. 

For spells, I would highly recommend you NOT give the dragon spells like Fireball that are focused on dealing damage. The dragon already does decent, consistent damage, so the benefit of a fireball is actually fairly small. You want spells that either increase the dragons action economy, or that allow the dragon to manipulate the battle, mitigate incoming damage, etc. Spells like Darkness, Gust, or Poison Cloud can really limit your players ability to continuously focus-fire a dragon while spells like Shield, Shield of Faith, or Bless/Bane can give the dragon extra protection from what attacks do come their way. Even damaging spells that can be used as a bonus action or even a reaction will benefit the gold dragon WAY more than a lot of the big damage spells you might think of giving your dragon first. 

Episode 45 of Critical Role's second camapign pitted the party against a young blue dragon. No spellcasting and it was a real challenge for 7 players at roughly level 6/7. Young dragons don't get lair actions or legendary resistances or legendary actions. But they still have their breath weapon which makes them really formidable. Add to that the fact they can fly and suddenly your PCs who rely on melee are not able to do as much damage to the dragon. I would rely on terrain to up the challenge if you really feel you must but just being against a dragon is going to be a major challenge for your players.

I agree that young dragons don't get Legendary Resistances nor Legendary Actions. However if the Young dragon has been working on its lair for a longer period of time. Its presence will start to influence the surroundings. And he WILL have a lair action.