Being statute barred means literally that there is something in the law that states that after a certain period of time you can not be prosecuted.
There are restrictions which can apply, to how long after the commission of an offence, a person can be charged. The periods prescribed may vary according to the seriousness of the offence.
Generally, for summary offences, that time limit is one year. Time limits also apply in some sex offending cases. Where the allegations are historic, your lawyer should check the legislation to see whether the offence falls outside the prescribed time limits. If it does, then the charge would be statute barred.
Such statutes are enacted to protect persons against situations where evidence has been lost, memories have faded, or witnesses have disappeared.
Where matters are quite dated, the legislation ought be consulted by your lawyer, to see if the defence of statute barred is available to you.
This sort of defence is very technical and is something that you should be discussing with a lawyer as soon as possible.