Its a good game, or at least was last time I played it a few years ago. For a 5 year old? No, pretty much any online shooter is going to have voice chat and you're going to be at the mercy of whatever randoms on there have to say. I wouldn't let my 5 year old play it anyway.
It is actually quite beginner-friendly for a 5yo old if you give him your credit card and let him buy one of those 1500USD progressive weapon skins that you can get from the PUBG shop. It's shiny and it'll make him look cool on the battlefield. It is also absolutely fantastic for a young mind to get introduced quicker to the capitalistic world, not to mention getting introduced to violence and guns.