When I got my job 11 years ago I told them I was seven years younger than I actually am! I’ve had to keep up the pretence all this time, but I will be 66 next year and although I won’t have to retire my national insurance contributions will cease and my tax code will change. Is fibbing about your age a sackable offence?
Although dishonesty can be grounds for dismissal it’s unlikely the untruth you told at your interview will have affected your subsequent work. If you had claimed to have qualifications you don’t possess this may have affected your ability to do the work asked of you, but it’s hard to imagine circumstances where seven years’ added maturity will have prevented you doing your job efficiently. Just tell the personnel department their records are wrong.