A conviction for lewd and lib is held on the Scottish Criminal History System under their weeding policy of 30 / 70 which means at least 30 years and you must be over the age of 70. This can be extended if you carry out similar offences. Then the weeding will not occur until the new offences are weeded. For sexual offences it does not matter what age you were at the time of the offence.
If you want to dispute an offence you should contact the Force in the area where the conviction occured. There are required to investigate the dispute under the Data Protection Act 1998.