For me it's entirely up to how you define "backlog" I guess.
If it's just games I've bought and haven't played, I could realistically do it in a couple years. It's somewhere between 100-200 games and I generally play between 30-50 games a year (depending on the games I play. If it's lots of RPG's that number is closer to 30). My collection is actually not as massive as it once was cause I purged a good 50% of it like 7 or 8 years ago. I went from just collecting everything that looked interesting and putting it on my shelf to creating a highly curated collection featuring only my top 50 games on each system. So I've actually beaten a good 90% of the games in my collection, with most of the unfinished ones being games I picked up in bundles on Steam.
But if you broaden the definition to just "any game I want to play but haven't", it will take much, much longer. I am constantly looking for new games to add to my collection. It's really fun for me to find a game that makes me rethink my collection. Like "if I add this to my collection, what will I take out". On top of that there are systems I haven't really collected at all yet like the Famicom and Super Famicom, So I'll probably have to play through 100+ games before I can settle on my top 50 I actually add to my collection.
