Adobe Photoshop Elements 2019, US$ 100
The system requirements list
✓ Windows 7 with Service Pack 1
✓ 64-bit versions only (32-bit not supported)
✓ processor with SSE2 support (the i5-2450 has SSE2 support)
✓ 1.6GHz or faster
✓ 4GB of RAM (8GB recommended)
So you're well above the minimum requirements.
would run very fast on my system
Well, that's not possible to tell, to be honest, because that depends
a) on the hard disk drive type. An SSD may speed up things by a factor of 10
b) on the size of images you edit.
c) what you define as very fast (may be much different that what I think is very fast)
Let me elaborate on b) for a moment. You have 6 GB of RAM. 1 GB will be used by Windows on its own. The remaining 5 GB can be used by Photoshop. 2 GB will be needed by Photoshop itself for the windows, menus, pens and brushes etc. The remaining 3 GB can be used for images.
If you want to be able to to 19 undo steps, there's 150 MB per image. An RGBA image has 4 channels, so you have 37.5 MB per channel. This means you can edit images up to √37.5M ~ 6000x6000 pixels.
It should be sufficient for
some basic training on Photoshop