What is the maximum attainable level?
It's 100 (120 Skill-points)
Sources:
CONFIRMED: Level Cap
What will be the max level in the real game?
Highest level on payday 2?
Whats the Max level achievable now?
According to the achievements board, the current level cap is 100 (cf. Most Wanted achievement).
You earn one skill point per level and two additionnal skill points every 10 levels for a total of 120 skill poins.