Is the fact that he held similar positions 35 years ago supposed to be some kind of gotcha? People can change a lot in that amount of time.
Not to mention, the government and laws have changed a great deal. Increases to retirement age were passed and have been phased in, like Biden wanted, so it isn't necessarily a "gotcha" that he is against further increases to the retirement age.
We also see a change, even in CNN's video when it comes to sunset laws -- it would appear he realized that some programs, such as social security, needed to be protected from sunset laws; hence the difference in the proposal he made in 1975 vs the one in 1978.
And all of this ignores the issues with politics today. In the 70s, and even the 80s, both parties still attempted to work together for the good of the nation and there was a serious hope and belief that both sides would work together and compromise to keep vital programs funded. Today, from what I can see of Congress, there is no such hope and a divided Congress, faced with a "sunset," might rather see the government fall than to give a "win" to the other party -- particularly if it is Republicans refusing to vote for various entitlements, the IRS, the DoJ (so long as there is a Democratic president), and FBI; or Democrats refusing to vote for various multi-billion dollar defense programs or programs that largely benefit agricultural (Republican) states.