A 5 year old computer is something of a gamble - it might last another 5 years or it might die tomorrow. This might also be said of a newer computer but once Apple declares a computer to be vintage getting it repaired can become quite difficult. A 2012 isn't vintage yet but Apple will probably declare it so next year.
The 4GB RAM isn't a major problem as long as you don't intend to run lots of heavy duty programs - I was amazed at how well my 2011 MBA ran current software. What does give me pause though is the 64GB SSD. The OS is going to take up about 20GB and it is best to allow at least 5GB free for temporary files, etc. which leaves about 39GB free for applications and data. That is much less than you might think. You can pretty much forget about keeping music, videos, and photos on it.