You have to recognize what the enemies pick from champ select.
Yi, Tryndamere, Vayne, Riven, as well as Yasuo, Jax, Fiora and Nasus are all late-game scaling hypergods of death.
You will not and cannot win against them in the late game. That's why they'll try to either get an advantage early, in which case you simply ff@20, or stall out until 35 mins.
Now, what can you do?
Well. You either pick champions with earlier powerspikes and end the game before it gets to 40 minutes, or you also pick late-game champs to match their strength and try to race against them into the lategame.
Champions with early game powerspikes are the likes of
,
,
,
(very risky pick, you HAVE to win lane with him),
,
etc.
The goal with them is to destroy everything that's in front of you as fast as possible and end the game at 20-25m before the enemies get a chance to scale. You have to be absolutely relentless- gank ALL the lanes, take ALL the objectives, push ALL the turrets, invade ALL the junglers. It's a race against the clock, and the enemies WILL try to stall you. Which is why early game champions usually work better in the hands of experienced players that know exactly what they're doing.
You literally have godmode for the first 15-25 minutes of the game, you CANNOT afford to waste any second of it. If you think you're ahead and relax, you've lost. If you're pantheon, you kill the enemy fiora 7 times top and you do NOT end the game by 30 minutes, you WILL die to her. Even if you were 14-0 early on.
This is also similar with mid-game champions (which is the majority of them), however it's much less extreme. You will still lose against late-game champions, but at least you have a fighting chance and it comes down to skill much more.
However, the problem with Trynda is not only that he scales very well, but that he's an immovable splitpusher as well. He will keep pushing the lane relentlessly and you can't either fight him or stop him.
These kinds of laners are VERY hard to deal with without coordination. You can't really fight him with anything post 6 if he's ahead, even or even moderately behind. You have to be either out of his range completely, or MILES ahead.
So you have only two options: either pick a siege champion, or absolutely overwhelm him with the help of your team.
If the jungler ganks the shit out of top lane before he's lvl 6, and he dies a few times, he reaches a point where even with his ulti, he can't kill you. And if he can't kill you, he can't push- so he's ruined. He can't do anything else. Trynd can't teamfight for shit, he can literally only splitpush. If your jungler is not braindead, he'll gank two times every minute until Trynd is begging for mercy. This is the best option.
Unless he's left to farm, he will never come back into the game. There's nothing he can really do at that point except from coming back to lane and dying.
The other option is better for lower ELO where you are more likely to fuck up the matchup. Pick a ranged champion that can poke and kite him safely, and poke the shit out of him.
Gnar is a good option for top, because you're still a great melee beast for your team. Also, his erratic changes from kiting to aggression can catch Trynd off guard, allowing you to waveclear with Mega form and then back to poking. Then, what else... is Vayne top still a thing? That should work too. Anything with safe, overwhelming poke or waveclear is great.
Finally, there ARE some laners that can face Trynd 1v1 and win, but it's not easy.
Top lane tanks like Rammus or Naut can simply tank his DPS as long as he's not ahead.
Darius can play around his dunk and either dunk him before he ults, or bait Trynd's own ulti with it.
Then there's Irelia who can destroy his face easily but she needs to be ahead and play smart. I also destroyed a Trynd yesterday with Camille, but I was so ahead of him that half the times he didn't have the time to ult. :P
Garen can also dunk him before he ults, and generally go toe-to-toe with him rather easily.
And finally you can also play an immovable splitpusher yourself. Olaf, Shen, fucking Trundle, Kench, Poppy etc. Tanky as shit, most of them have decent waveclear or build one of the Hydras (or both), half of them can let Trynd hit them for his entire ult and not even give half a shit.