You can't just add the figures up can you...you need a NPV analysis as the value of £6500/month 25 years from now isn't what its worth today.
Let some of the old guys tell you what their cash was worth 25 years ago?
Of course if you assume your pay rises keep pace with inflation then the "real" value of the cash is maintained.
But that certainly isn't the case with my pay packet over the last 10 years!
Lastly, but not leastly, if you're able to pay your £400K/20 years mortgage off 10 years early by earning earlier in your career rather than later, you'll save yourself...about £125K if the interest rate is 5%.
At 10%, you'll save yourself £289K.
Statistically, with health issues being more likely to rear their ugly head in later life, earning early in your career in such an uncertain world has got to be a good thing.
If the break-even point was age 50, rather than age 60, different ball game.
FWIW.