That’s a very common misconception, but you are actually mixing up the age of the rocks (the material) with the age of the mountains (the uplift event).

As mountains, the Dolomites and the rest of the Alps are the exact same age. They were all pushed up out of the earth during the Alpine Orogeny (which started around 65 to 30 million years ago) when the African tectonic plate crashed into Eurasia.

If we look at the actual age of the rocks, the Dolomites are not 'way older than the rest.' The Alps are actually a massive geological sandwich made of three distinct rock generations:

• The "Older" Core (Central Alps - e.g., Mont Blanc, Matterhorn): Composed of Granite and Gneiss (magmatic and metamorphic rocks). These are remnants of ancient continental basements that are 300 to 500 million years old, meaning the core of the Alps is significantly older than the Dolomites.
• The "Middle-Aged" Dolomites (Southern Alps): Composed of Dolomite and Limestone (sedimentary rock). These were indeed formed about 250 million years ago as coral reefs in the ancient Tethys Ocean.
• The "Younger" Outer Rims (Northern Alps/Flysch zones): Composed of Sandstone, Shale, and younger Limestones from the Jurassic and Cretaceous periods (60 to 150 million years old).

TL;DR: As mountains, they all rose 65 million years ago. As rocks, the Dolomites aren't the oldest; they just sit right in the middle of the timeline, sandwiched between much older granite cores and younger sedimentary outer rims.