If you use 18-20 years as a benchmark, you’ll be about right. It may go slightly more junior than that but it’s the holy grail for most people so don’t expect it to go wildly junior. My first opportunity for a LH command was at eighteen and a half years. It’s currently sitting at about 18.
I do do a lot of short (three day, two crew) trips on the 400 but that suits me. The senior mostly seem to head for South Africa.