I shared data on this for the US before, but here's some UK data as well. You can see it via ideological self-identification as well. There's of course plenty of time for things to change, but what we've seen so far is that Millennials aren't getting more conservative as they age. If anything the opposite.
This is well captured on specific issues too. Millennials have gotten more liberal on abortion as they've aged.
The politics during early adulthood are pretty formative for generational politics (and within generations). For Millennials this was Bush, 9/11, the Iraq/Afghanistan wars, and the Great Recession. So I suppose it isn't too surprising that they are bucking the trend.
I think this a direct result of the internet and social media. Older generations got soundly into their little news bubbles before the internet arrived, and once the internet came around they rejected what they didn’t want to hear. (I mean, I did that quite a bit. But I’m much more widely traveled than the average person. I came around.)
Millennials had it from early on and have less of a news bubble. They have more friends in a variety places in their life. Also they have probably learned how discern BS better.
Obviously a gross generalization, but I think it does apply to enough that it greatly sways the numbers.