There is no cap on attributes, other than the technical limit of storing the values in 4 bytes in one of the save files. Actually, you can not max (FF FF FF FF = 4,294,967,295) the stat values; you can get up around 90 million, but closer to a billion there start to be issues (with strength, for example, the weight capacity becomes negative, and at higher values the strength itself becomes negative).
Practically, though, you are limited by level, equipment bonuses, the number of charm slots (up to 5 per piece of equipment, with up to 10 stat points per slot, using gold charms), etc.
At the end of my first game my stats were as follows (the number in brackets indicates the values with no equipment, without Finnigan's lockpicks in my inventory). I had plenty of gold charms I could have used, if needed.
Level 53 Warrior
Vitality 1260 (444)
Magic 574 (30)
Strength 145 (111)
Agility 150 (112)
Intelligence 18 (10)
Constitution 100 (74)
Offense 124 (89)
Defense 108 (78)
Damage 139-178 (54-64)
Armour 484 (0)
Lightning Resistance 95 (25)
Fire Resistance 110 (25)
Poison Resistance 35 (25)
Spirit Resistance 95 (25)
Reputation 51
Weight 4500 (3820)