Here we go again.........
Cheques are NOT invalid after six months, though depending on the individual bank involved, it may have a policy not to honour them outwith that time frame, or not to do so without checking first with their customer. Legally cheques are valid for six years.
There is a every chance if you bank the cheque it will go through successfully but it would probably be safer to contact the company directly and ask for a replacement.
For what it's worth I have often seen cheques more than six months old clear a company bank account unchallenged by either the payee or payer's bank.