Time is a factor but not the single
or most important one. Proper rig tension is very important. Sailing for two years with loose rig can cause more damage than ten years sailing under proper tension.
Check all fittings with a magnifying glass, looking for cracks or stretch marks. Check connections between fittings and wires for rust. Any single
broken strand on the wire requires full wire replacement.
Check fittings connection to mast
and chainplates for stress signs, rust, cracks in fitting or weld, elongated rivets, bubbles of paint
There is special spray to be used on fittings for cracks finding.
Check spreaders ends for integrity, spreaders angle to the mast/wire.
Check sheaves for wear.
There is more to the check - any experienced rigger will do a proper investigation - if he recommends replacement, you may interrogate him to show you the faults he has found. Age in itself when everything seems OK is a reason only if really extensive (12 - 15 years?)