Not sure if above response was tongue in cheek, but: in the US almost no airline employees get a pension anymore, so that has nothing to do with it. It's mandatory in the sense that you can't work any longer when you reach age 67, even if you wanted to. It was being lobbied for by the US airlines to reduce the training costs associated with recruiting and training new joiners.
I don't believe it's wise or necessary to increase the mandatory age to 67. The much touted "pilot shortage" will be staved off by the somewhat perilous present economic situation; cargo carriers are now struggling and some low cost carriers like Spirit are on the brink of bankruptcy. Furthermore, on average (yes, there are exceptions), physiological characteristics such as endurance, reflexes, and capacity for learning undoubtedly decline with age. Selecting pilots to remain past 67 would probably necessitate increased medical examination scrutiny if present safety levels are not wished to be eroded.
Lastly, yes, many pilots already had to sit through 5 years of seniority stagnation 15 years ago when the mandatory retirement age was raised from 60 to 65. This also ocurred during an economically unpleasant time. The experience of junior pilots during this time perhaps inadvertantly contributed to the present alleged "pilot shortage", as many pilots became burnt out and likely dissuaded younger acquantainces from pursuing the profession. Why repeat that ordeal just to appease the perceived very slight training cost reduction for the US airlines which are brib....I mean lobbying the US congress to get this passed again?