i am looking to buy an A1224 in core 4GB 160GB HDD OS X El Capitan for my son for Christmas. he wants to create music on it. what software will he need and is this too old to support it?

I know this may not be the answer you want, but please don't buy that Mac. It's too old, and will just result in frustration for you and your son.

If you want to save some money buy a Mac from Apple's Refurbished and Clearance page. You can also get discounts for education.

You can certainly consider used Macs, but please shop from reputable sellers. OWC has an impeccable reputation: https://eshop.macsales.com/shop/Apple_Systems/Used/Macs_and_Tablets.

OWC is not the only reputable seller of used Macs. They are one of very few I am comfortable with recommending personally.

Avoid eBay. Even though their buyer protection guarantee is solid, I estimate 99% of eBay sellers fail to properly prepare used Macs for sale. Again, that results in wasted time, effort and frustration for buyers and sellers alike.