It's okay but it only has PCIe 2.0, iirc now the default is 3.0
Also you can build a very capable pc for $600 without having to go used with old hardware. If you want a list, I could make you one
The differences between PCIe 2 and 3 are ridiculously minor (5 fps, maybe 10 at most) though for a budget PC you could care due to the limited hardware, you're not going to feel it anyway in the long run.
- Intel Pentium G4400 @3.3 Ghz (CPU)
- MSI GTX 1050ti OC 4GB (GPU)
- G.Skill NT 8GB (4x2) DDR4-2133 (RAM)
- MSI H110M Pro-VD MicroATX (MOBO)
- Western Digital Caviar Blue 1TB 7200rpm 3.5" (HDD)
- EVGA 430w 80+ White (PSU)
- Corsair Carbide 88R MicroATX mid-tower (CASE)
I would not advise getting a Pentium by a long shot regardless of your budget.
I believe the GPU is a good decision, it's fairly cheap coming from Nvidia and will manage on your system, although it's not going to deal extremely well with High-Max 1080p gaming despite what INH said.
G.Skill for RAM is overkill. 2133 at that too, you can save a fair amount of money of getting another brand and maybe 1333 or 1600 mhz, putting more money into the CPU.
No comment on the mobo itself, although if he can get one for free I believe it should be the base of a budget build. The only issue is the CPU limit, but since he's on a budget an AMD for a CPU would not be the end of the world.
Plus if you have a PC already you might have salvageable parts that might not be a loss to replace with cheaper versions, such as storage.
Despite what I said about the RAM here's Nvidia's own suggestion, having randomly stumbled over the page.
http://www.geforce.com/whats-new/guides/geforce-garage-build-an-entry-level-geforce-gtx-1050-gaming-pc-for-only-500