I actually differ on this point. If making a dwarven mage, I make the CON score his HIGHEST stat, rather than his lowest. Hence, even if I only have a 14 or 15 for INT, then I can still raise it via magical items and via the Ability bonus for each 4th level. Even with 14 INT, he can still get all his top level spells until 11th level (which goes away one level after that) and 18th level, specifically. With INT-boosting items, this can even be further done away with.
However that 17 to 20 CON will be with him his whole career, increasing his Hit Points by 75% to 100%. Plus, higher concentration checks and higher fort bonuses add up to one hideously tough character, for a mage.
One of my favorite recent characters was a Dwarven Evoker with a 20 CON and a 16 INT. Thanks to the extra spells per level, I really didn't miss much, and thanks to the CON, I could contemplate my navel in a hailstorm.