Is my hardware too old to start tinkering with OSs?
I don’t know what you have but I’m using an Acer Chromebook from the early days, it’s one of the few ones which had Hard drive bay. I upgraded it to 8GB of ram and it works well enough for web browsing and even Minecraft (lowest render distance running optifine, forget about servers). Also windows wouldn’t run on this thing even if I wanted to, because it doesn’t have proper drivers for it and is way too slow for modern versions to run smoothly anyway.
Generally Linux supports much older hardware than Windows does but if it’s too old you are better off replacing said hardware with something slightly newer. Some old hardware is best suited only for Retro applications such as old-school gaming or running legacy equipment.
Will losing touch with the Windows environment make it more difficult for me to succeed in a Windows-dominated career?
Depends if they require it and how much or why they do. If it’s required then yes, if you can work around it then not necessarily.