The starting point for a section 18 is now 8 years since April of this year.
If this goes to crown court, he could be offered a plea bargain for e.g section 20. Obviously as he is innocent he won't be taking this in which case it will go to trial. If he is found guilty he would definately be looking at a few years.
He needs to speak to his barrister who is the best person to advise him.
If there is no forensic or dna evidence he may be lucky and walk away from it but be warned, it doesn't always go like that. The courts and the police in particular just seem to do what they want.
Good luck!