Experience 4 (Source)

The way level works for groups is different than for an individual PC or pet. When you group, all members of a group are treated as having the same Group Level for the purposes of /con and mission difficulty. Group Level is figured by the following formula:

(sum of all levels in the group)/2

In your case, your normal challenge level is 14. Your group level when with your pet is (14+10)/2 = 12.

Basically, for groups of 2, having a group member or pet with a lower challenge level than you will bring down your group challenge level below your solo level.

Just FWI, max challenge level any character can get solo is level 25

well, the level 25 thing only refers to your character's challenge level (IE if a ranger could /examin you the same way they /examin critters, the max level he'd ever see would be 25)

But the difficulty level you get at mission terminals depends largely on the planet and the terminal, as well as your solo and/or group challenge level.

Artisan and entertainer missions NEVER have a challenge level about 1. On some of the harder planets (Dathomir and Endor) you can't get missions below a difficulty level 35, even if your character's/group's challenge level is below 35.

yes, it is always divided by 2. I think it's supposed to be an incentive to grouping with more people. Course two people plus pets usually make up for that

Just some interesting numbers I cranked out when I was bored:

Max level of a group of 20 with no pets: 250 Max level of a group of 10 MCH with level 70 pets out: 475 Max level of a group of 10 Imps with 1 ATST out each: 750

Of course, there is an invisible cap when it comes to difficulty levels of missions. Depending on the planet, after a certain difficulty level, mission pay-outs no longer increase, and the size of the lair also remains constant. I think Dathomir is capped at level 60, but I haven't done missions there in a while. (IE every mission of difficulty level 61+ gives the same payout and has the same number of opponents as a mission of level 60 difficulty)