I'm 61 and fairly fit. My job is a mix of desk work and managing events.
I have no issues working at the moment and could probably manage another 10 years if needed. However, I run, practice martial arts, eat healthily, drink very little, have never smoked and my BMI is low twenties.
I wouldn't want to try doing a heavy manual job at 70.
More likely they will raise the required number of NI qualifying years from 35 to 50. That way, if someone starts at 18, school leavers will work to 68 and graduates will wait until 71 but, having higher earnings, are much more likely to go earlier and self fund. That would plug the funding gap by ensuring people contribute enough.
I worked from 16, while still at school, and all through my degree, and so already have 45 years, so would need another 5 years.