Q: Buying a used Ipad - software question

If you intend to buy second hand, you should look at iPad 4th generation or later model.

The coming iOS 10 will not support the 2nd generation iPad.

Here are things to look out for in a second hand device, see link below:

What to do before selling or giving away your iPhone, iPad, or iPod touch - Apple Support

The second Gen iPad will not be able to update to iOS 10 when its released. Whether this will cause any immediate issues for you is not something we can say.

Some Apps may begin to require the newer version of iOS after its released, and while you may be able to get compatible versions of the Apps for it, there's no point in starting with such an old device.

I would go for something slightly newer if only to be able to update for a while longer.

Look for at least an iPad 4. 

Also, some things to be aware of when buying second hand iOS devices in the following link:

what-to-do-when-buying-second-hand-ipad

NOTE: I AM AFFILIATED WITH THE WEBSITE AND I MAY RECEIVE SOME FORM OF COMPENSATION, FINANCIAL OR OTHERWISE, FROM MY RECOMMENDATION OR LINK.

You're welcome.