If you are in Anemos then doing the Notorious Monsters will allow you to level sync, hell you can even join higher level players in harder NMs and still get rewarded sizable exp (as long as you deal some kind of damage to the target). The challenge logs are more restrictive but it's common to find players out there that are trying to complete it around your own level, and once you have done it for the week then generally it's straight to the NM train anyway.

Pagos is somewhat different, (although this setup might change in a months time) as most players are chaining mobs rather than NM stuff, so it can take a while to level up here unless you are able to find a nice party around your level. It might be worth stating in Anemos till a few early 20s, and then popping in to Pagos for the challenge log (or stay in with a nice party for a while). Should be plenty of time to catch up before the last installation of Eureka I think