The issue with a lower level pet and higher level hunter is that it’s slow going grinding mobs without the pet’s DPS and aggro to keep them at range.
I recently did the grind with a Worg from SFK for his 1.1 attack speed. It was level 19… and I was 37. (I had also just tamed Brokentooth… but we were same level so no issue there.
You have to kill mobs that are at least green to you… and the lowest you can go is 8 levels lower. Initially this is exactly what you want to do… Why? so you can kill it faster… a the pet will miss it’s attacks and cannot keep aggro.
Once you get within 11 levels of your pet… start killing mobs 3-4 levels above your pet… they will be within 8 levels of you then… but the pet can hold a little aggro and allow you to kill it faster and gain more EXP.
The more EXP YOU gain, the more it gains. So rested XP is VERY desirable… as you get double XP from those green mobs at first.
Another tip is to try and find areas with ranged mobs like casters, archers, or spear throwers. Why? Because they stay at range, and you put out more range damage than melee. They often have less armor so die faster. For example… Naga casters are good… they’ll hit you for nothing and die pretty fast. Don’t let your pet die… a dead pet will not get the EXP for the kill.
The fastest method is to run instances with a strong group… ones who could do well even without you there. Put pet on passive and stay well back form the group. You will get the most EXP, and thus so will your pet, with the least amount of negative effects from having to solo melee mobs.