First, I'll go through the individual Pokemon. I'll assume this is Gen 4.
Tyranitar
DDTar is a good set, but not early on. There's really nothing this can accomplish in the lead position besides starting up the sandstorm which honestly hurts some of your Pokemon more than it helps them. This is something to save for later in the game. Also, you'll probably want the item to be a Babiri Berry since nothing on your team lures Scizor very well.
Infernape
I personally don't like the set but I'll leave it up to your judgment since you have more experience with this team than I do. I guess my gripe with this is that I don't know what it really does to help your team win. But perhaps that's being nitpicky.
Shaymin
That's really not a reliable set at all, the Life Orber is proven and I do believe that some of our users used the Leech Seed set to success as well. Since this team's focus appears to be doing damage like any offense team, the Life Orber is probably your best bet:
Shaymin @ Life Orb
Trait: Natural Cure
EVs: 4 HP / 252 Spd / 252 SAtk
Timid Nature (+Spd, -Atk)
- Seed Flare
- Hidden Power [Fire / Ice]
- Earth Power
- Rest
You'll definitely want HP Fire since nothing on your team takes on Scizor well. Metagross can at least take Outrages from Dragonite and Flygon which makes HP Ice less appealing though ideally you'll want to replace your weak link to cover some of these weaknesses, probably with a Choice Scarfer.
Kingdra
Double Dance is a pretty underpowered set, and Rain definitely inhibits Infernape. You should probably just run Substitute or Hydro Pump in the last slot. Hydro Pump will probably require different EVs though. You could also use a bulkier set like ChestoRest Kingdra to help tank Starmie better, as it's the only Water your team can't handle (Shaymin handles the others reasonably well). Also, you probably should use all 510 EVs =p.
Metagross
The set works, just make sure that you lead with it over Tyranitar. Otherwise you're probably better off using something like Swampert. As for the item, I prefer Lum Berry because it beats those stupid sleep leads, and even when you don't face one, you can bring it in to absorb status just once, but that just once is often a lifesaver, especially against something like a Machamp DynamicPunch. I've been saved against Machamp a few times by Lum Metagross, and that's good for you since you lack a Fighting resist.
Aerodactyl
Taunt over Fire Blast really helps you with stall teams. Other that that, it's fine, though you might as well use Pressure instead of Rock Head (Rock Head doesn't cancel LO recoil so it's useless).
As far as the overall structure is concerned, it's pretty potent offensively. There are a lot of dangerous sweepers that will give your opponents trouble if you hit them before they hit you. That is a pretty big if though, so you should be prepared with a little more defense probably.
Whatever you determine your weak link to be (my guess is probably Infernape), you will probably want to replace it with a Choice Scarfer like Flygon or Jirachi. This will help your team against dangerous threats that you currently have trouble with, most notably Gengar, Dragonite, Gyarados, and Lucario. If you can fit it in, a Fighting resist is also highly recommended to deal with strong attacks from Breloom, Machamp, and Lucario. The best of these is probably bulky RestTalk/Waterfall Gyarados with either Roar or Dragon Dance in the fourth slot. I would suggest DD if you do opt for Gyarados if only because it gives you a win condition against stall teams. Of course, replacing Pokemon is difficult. Replace what you want, but my suggestion is to replace Infernape and maybe either Kingdra or Tyranitar if you want to fit in a wall Pokemon with your Scarfer (should you decide to go that route). It's really up to you.
But this isn't a bad start at all.
