So, what other languages became available in 1961?
The first that comes to mind would be COBOL as there was a 1961 definition/version.
But all the way back than it gets hard to tie a language to a certain year, as "Software as a Product" wasn't really a thing - and thus sales dates are rarely available. Similar for release dates, as that was often a gradual process involving user feedback (*1).
Also, if I understand this challenge right, any language available in 1961 will do, wouldn't it? So pick any with some date before 1960 - like COBOL-60 .. ups :))
I'm trying to get Programming Languages Through The Years over on the Code Golf site going again.
I think the 'at least 5 years older' clause makes it hard to come up with more than a few iterations. Trying to eliminate that for anything before, lets say, 1970 could be helpful.
*1 - In fact, what I so much love about today's open source development cycle of putting stuff on Github, having users play with it, supplying comments and patches back into the main branch, is quite much like software development originally worked. The way it always should have been. Now supported by the internet and complex tools instead of sneaker-net and card punches.