The score grows with continued play and can drop if a player gets demerits or bans.

You can check your own oldtimer score progress by opening your player profile, clicking the edit button, and looking for the “Progress to next” bar.

Also, only a subscriber is considered as a "Premium Member".

Oldtimer Score (Level 1–9) - how to level up

The score is primarily based on total playtime—so to level up, simply play the game/s.

The Oldtimer Score is a system designed to reflect a player's commitment and conduct. It ranges from level 1 to 9 and serves as a visible indicator of a player's long-term engagement and behavior.

Demerits can, and bans will negatively impact the score - points are deducted accordingly.
If all points are lost a player is back to level 0. The score can be restored by continuing to play and maintaining a penalty-free  over time.