Question about specific ipad trade-in

You can verify eligibility for trade-in and obtain an estimate of the potential trade-in value here:

Apple Trade In - Apple

You should be able to trade-in at a physical Apple Store - many choosing this option by preference as the device can be checked, the trade-in value finalised and the process completed while in-store. Be aware that Apple’s in-store trade-in values may differ from the on-line estimate.

Before parting with your iPad, whether trading-in or selling privately, ensure that the device is properly prepared:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

You are posting to a user to use, community forum and do not even tell us the model or OS of your older iPad. This is the best we can do. Did you try LotusPilot's first link? If you need an exactly answer of what the trade in value would be for your specific iPad, you have to take it to an Apple Store, as he mentioned. They will look at the physical condition and run diagnostics ... then they can give you the specific answer as to the trade in value of that older iPad.