[ArM5] Affinity, XP and Limits clarification?

[John Buston]

Just to make sure I have interpreted the rules correctly is the following 
example true?

A magus, let's call him Darius, has the virtue Affinity with Perdo.

He currently has zero in Perdo (it's a simplified example).

He studies for six seasons from a Perdo Summa which is of level 16, quality 
15.

Therefore he gains 15 * 1.5 (affinity rounded up) = 23 xp in Perdo per season 
until he reaches level 16.

After season 1 he has 23 xp in Perdo; he has Pe at level 6
After season 2 he has 46 xp in Perdo; he has Pe at level 9
After season 3 he has 69 xp in Perdo; he has Pe at level 11
After season 4 he has 92 xp in Perdo; he has Pe at level 13
After season 5 he has 115 xp in Perdo; he has Pe at level 14
After season 6 he has 136 xp in Perdo; he has Pe at level 16

So he has gained 136 xp and 16 levels in Perdo in 18 months.

Have I missed a limit anywhere?