Why do any of the young dragons don't have a STR Save listed? It should be at least the STR Mod, but since apparently they have proficiency in all their other saves it should be prof+mod. 

The saving throws only indicate its proficiencies. If it makes a Strength saving throw you add the corresponding stat modifier to the roll.

I think you may have suggested that, but it was unclear.

Their saves in their stat blocks are for saves they are proficient in.
For example despite having 10 dex, meaning +0 dex mod. They still have dex save prof, which we can determine their proficiency bonus as being +4 since that is what their save shows.
That's why my dude.

It do be lookin kinda fresh doe

I`m making this Red Dragon that is really big and strong for his age.  For example he is young, but has the stat block of an adult.  Thus if he was an adult he would have the stat block of an ancient.  Is this broken or is this within the rules?

I'm new and I'm about to fight this guy for xp. So excited.

I think given the variety in shapes and sizes humans have, this would totally work. Dragons can grow in different ways. What do you plan to do when he's an ancient dragon, though?

As he gets older he will gain class levels, thus when he becomes ancient he will be very powerful.  Plus his heritage will be a great shocker to the party.

why are there no comments ancient had like 100

man u the dm, do whatever floats ya boat

What does recharge 5-6 mean?

For any creature that has a combat ability listed like that (Recharge 6 or Recharge 5-6), it works like this:

The creature can use it as its action (taking the normal action, so for the young red dragon, this would be instead of doing bite/claw/claw attacks) for the first time whenever you want in the fight. First turn, or once the heroes close with it, whatever.

Once you've used it for the first time, you roll a d6 on future rounds to see if that ability recharges. So if you have the dragon breathe fire on round 1, then when its turn comes up on round 2, you roll a d6. If it comes up 1-4, the fire breath hasn't recharged yet. If it comes up 5-6, it has recharged, and you can use it that turn (or the turn after that, or after that, whatever). Once you use it again, you have to roll recharge to get the chance to use it a third time.

It adds some randomness to fights. Really unlucky parties might have that dragon breathing fire on them a bunch, while lucky parties might only have it breathe fire once and then get some bad rolls for the next few rounds.

Hope that helps!

i need help im the dm, a bard player got a nat 20 on befriending this

Just remember that any roll even a crit on a persuasion check doesn't change the nature of the dragon. It might look at your player and not want to kill him right away, maybe even give him a quest or see him as a potential subject. However, this wont make the dragon friendly, it wont make the dragon fight for them, or go out of its way to help. TYPICALLY red dragons are greedy, evil, and generally all-around bad.. So that will remain constant. 

Is this the youngest version of a red dragon?

The breathe weapon will recharge on a 5 or 6 on a d6 dice roll.

I'd probably still use the normal stat block for basic rules but modify strength and constitution for the indivdual.

isnt this just small red dragon?

Red Dragon Wyrmling