old car, also a car that has been driven hard will have softer seals,hoses,and just generaly abit worn in all the hydrolics. also using a "performace" brake fluid also softens the seals making the pedal soft aswell.
unfortonatly there isnt much to do about it. sometimes its air stuck in the abs unit. and sometimes its just a case of soft seals. new pads feel soft untill fully bedded too. using a bigger master cylinder is a option. but you have to swap over the proportoning valve in the origonal cylinder or you will crack rear disks and or overheat the fronts.
oh and pad knock off from wheel bearings is pretty common. especaly if you have bigger disks fitted.