Is 2.5 too old to sleep train?

[LittleLadysMama]

I feel like I saw lots of articles about sleept training for babies, but my DD was thankfully a great sleeper (regressions aside!) so i didn't need to consider it. She's now almost 2.5 and my great, 12 hours a night sleeper has turned into a tiny sleep theif 😴
She used to nap in her cot and self sooth until around 14 months but has always been held to sleep in her room. Usually a 30 min cuddle max and then she could be put down asleep. Always knew this wasn't ideal, but it worked for us, and once asleep she slept through 🙌
Now, she still needs held to sleep, will NOT lie down willingly, doesn't just cry but screams and wails and stands and jumps and protests to the point She's likely to hurt herself with her antics. She's waking through the night too, bedtime around 7.30/8 and she can be up anytime from 11 til 3am. Will calm if picked up but can try and settle for hours and still won't let us put her down in her cot at that point, asks to come into the 'big bed' instead and sometimes we cave in (not ideal, I know), just so we can sleep and function 🤷‍♀️
I've been hoping it's a phase but truly starting to think we have an ongoing problem now and don't know if there are any sleep training options at this age we could try?
For info she still has 1 nap and sleeps in her cot, doesn't climb out, just gets very mad if she's in there and awake.
Any thoughts, experiences and advice welcome 🙏

No, not too old.
At 2.5 she's a bit old for a cot (unless there are additional needs, of course). Treat her like a big girl and make a big fuss about getting a big girl bed. Let her choose new covers etc and buy a Gro Clock (make sure you read the story, it's important!). Get a sticker chart and explain that each time she stays in bed, she'll get a sticker. Let her choose a toy / comic / special treat for completing a row or 5 stickers / 10 stickers / whatever your target is.
Then take her to bed, cuddle, read stories or whatever you choose for your routine. Make sure she's not over-tired. If she gets up or cries, stay calm and go back to her but don't engage. Just a simple 'it's nighttime, back to bed' and put her back. Repeat (probably lots of times ). Don't shout, no lights, no chit chat. She'll soon get the idea. Give lots of praise in the morning for a successful night.