Project CARS 2

Final solution now:
The license achievements are tied to online races.
To unlock the Veteran License you need about 350 completed online races.
When boosting this together with "Safety First" you're looking at roughly 15 hours of boosting, as 10 lap races take about 3.30 minutes with loading times and the 1 lap race approx. 1.45 minutes.
When trying to do this legitimately you're facing at least 100 hrs+.

Here are the most important settings when creating the lobby: (not mentioned is up to you)
Vehicle - Formula X
Track - Knockhill Tri-Oval
Race settings
Duration Type - Laps
Number of Laps - 10 for Safety First, when unlocked set it to 1
Start Type - Standing

Host settings
Privacy - Public
Realism settings
Damage Type - Full Damage
Force Cooldwon Lap - No
Opponent settings
Maximum Grid Size - 2
Fill with AI - No
Opponent Field Type - Same class
Rules and Regulations
Competitive Racing License - On -> very important, otherwise you wont make progress!

When you're boosting now first do 10 lap races until you unlocked the B safety rating for "Safety First", this should about 2 hrs if you start from U1500 (it will go up F, E, D, C and finally B, the number doesn't matter, it just means how fast you are compared to others)

When both of you unlocked Safety First switch the lap counter to 1 and go on racing until both of you unlocked Seen it All.

Side note: Both players should finish the race, otherwise the rating seems not to go up.

Credits: Credit goes to Boyd 12, AstroFlibble and NARIMANIK from the PST-forum, as they created and refined this method. Another credit goes to my fellow boosting partner Henry H8 who boosted this with me from zero to pop. :)

I do not take credit for the following solution, as I've discovered it on YouTube. Credit goes to Dzwienkoswit but I thought I'd share this for anyone who wants to slowly grind the 350 online races on their own, without a boosting partner:

Create online event
In host settings set privacy to PRIVATE
In Opponent settings set the following:
Maximum Grid Size: 3
Maximum Human Opponents: 1
Fill with A.I. Opponents: On
Opponent Skill Level & Opponent Aggression: 0 (not necessary but keeps A.I. out of the way)
Track Select: Texas Motor Speedway (the 1.49 miles one)
Vehicle Select: Up to you (I picked Formula A)
In Race settings set the following:
Duration type: Laps
Number of Laps: 1
Formation Lap: No
And finally in Session Settings set Practice to On (Duration doesn't matter)

With the above settings you can now press start and in the next menu you'll see that you have the option to start the race on your own BUT here comes the tricky part in which you need to act fast:

Press RB once so the middle box on the left displays "Practice"
Press Start (you'll get a 5 second countdown)
Quickly go to the "middle box" and press A to access it, turn practice to OFF and press save.

Complete the race and return to lobby. The practice setting will still be set to OFF, so in order to be given the option to start the race, you need to turn it on and save. Now repeat the process of pressing start, quickly hopping in the middle box to turn practice OFF and press save.

It's not as complicated as it sounds and it takes about roughly 2 minutes per race, so you're looking at close to 12 hours of grinding using this method to get the 350 online races done.

I hope this helps anyone who's struggling to find a boosting partner. Let me know if something is unclear about this solution and I'll try and help you.