The antifreeze itself does not degrade in that it will still not freeze at the temperatures advised re concentration.
The problem is that the anti corrosion additives stop working after a time.
The latest cars say up to 10 years old have about a 10 year antifreeze lifespan. Check that, as some makers have only used the advanced mixes and seals that work with these mixes for less years than that.
If it says nothing in your handbook I would use one of the 5 year mixes similar to Comma G30 or the equivalent Halfords product.
Again if your hand book does not give an antifreeze lifespan, I would drain, refill with water, run the engine up to temperature, drain again and refill with the antifreeze recommended by your supplier with an antifreeze content at 50% to 60% concentration or use an already diluted product.
