From your initial question you indicated your computer (laptop) is aged which suggests that it may be 32-bit rather than 64-bit. 64-bit is the latest technology for designing/building computers.
64-bit technology allows and uses computer memory in excess of 4GB RAM (up to 128 GB - an overkill) whereas 32-bit uses/allows/restricts a maximum of 4GB irrespective how much memory you have in the computer. FSX is based on 32-bit technology whereas X-Plane is based on 64-bit technology. So, if your laptop is 32-bit then I am of the belief that it will not run X-Plane.
If you want to stay with a laptop, to be used for gaming as well, you need to look at either a ASUS or MSI "gaming" machines, preferably 17 inch. One of the problems with laptops is you are restricted in the flow capacity of the builtin cooling fans.
One of the advantages of a PC is you can add additional cooling as and when required as well as upgrading your components at a future date.
For the amount of money you will outlay for a laptop you can build or have built a computure of much higher specifications.
If you want to become "serious" with flight simulation then go for a PC.
Again, I hope this helps.