You will probably be OK. What apparently happens to liquid malt as it ages is that it darkens, but in your case not likely to be very much, so the malt is fine
Your problem may be with yeast. Depending on how it has been stored it may have lost some of its 'potency' due to its age. The other problem is that Woodeford's (Muntons) kits used to come with only 6g of yeast and that is barely enough to brew 23 litres of beer, worse if it's old. However if you have 2x6g packets you should be OK
But with only one 6g packet I would advise, if you have access to a fresh packet of ale yeast, using that in addition to or instead of the original yeast, but if you don't have more yeast then you need to get the yeast going in a starter before pitching. So what I would do is to add about 100ml of cooled boiled water at about 25*C to a sanitised jug, add the yeast, cover with cling film then leave it for about 30 mins in a warm place, then add about half a tsp of your malt extract into the yeasty slurry, stir well, and leave for another 30 minutes in a warm place. By then the yeast will hav egot going properly and you can pitch it and hopefully you have given it the best start you can.