I was fortunate enough to retire at 55, mainly due to the fact that I was a director of a business that was sold a number of years previously. This gave me the dosh to pay off my mortgage just before I was 50 and I was able to invest a reasonable amount in the stockmarket that now provides me...
To be considered rich, one would have to have substantial assets as well as a decent income, either from work or investments or both.
An income of £50 k doesn't make you rich.