There are many pilots who love flying as a lifelong enjoyable hobby. It devasted me when I reached 60 - one day in command of a 737 in Europe and a few hours after midnight too bloody old. I used to laugh decades ago when I saw the quaint sight of an airline pilot on his last flight at 60 being pushed away from his aeroplane in a wheel chair by cheering and of course well meaning colleagues. Not now I don't laugh, because I think it is sad - and I suspect the wheel chair occupant secretly felt a bit glum deep down.
For those on huge superannuation payouts their financial future till death do us part, was secure. To those of us who were never in the big money making airlines we still need to eat. A long time ago, some research of other concluded that forced age 60 retirement of airline pilots contributed to early deaths than the norm for other occupations. I would not be surprised at that.
Of course pilots well under the age of 60 would like to see the old codgers of 60 thrown out to get the seniority system a chance. I was probably one of them, although I don't recall specifics. It is well nigh impossible for a younger person to conceive that an over 60 pilot would really love his job so much he would want to continue to fly aeroplanes and enjoy the view from 41,000 ft.
There is no doubt in my mind (and I am well over 70 and a reasonably competent flying and simulator instructor thanks to a kind gesture by various operators), that providing one passes the usual medicals and one demonstrates the normal competency in regular simulator proficiency tests expected of an experienced airline pilot, the age 60 rule means SFA as a cut-off age for a captain or first officer.