If you are not using any mods, just add [SKILL_RATES:100:NONE:NONE:NONE] to the dwarves entry and it will remove skill rust. Same with [ATT_RATES:500:NONE:NONE:NONE]
You do NOT need to regen a world for this to take effect; if you already have the world generated open up the save folder and add the line in the appropriate part of the raws.
If you are using a mod with a race that has a custom [SKILL_RATES:a:b:c:d] and [ATT_RATES:a:b:c:d] tokens, you need to find that and change b, c, d to numbers of your liking or to NONE to eliminate rust altogether. Dwarves will learn skills at the same rate as before.
Also be aware that there is a default cap on how far attributes can be modified from their starting values, which can also be changed.
EDIT: You may have to specify [MENT_ATT_RATES:a:b:c:d] and [PHYS_ATT_RATES:a:b:c:d] separately. Can someone confirm this?
[MENT_ATT_CAP:attribute token or ALL:%] and [PHYS_ATT_CAP:attribute token or ALL:%] control the level the starting stats can be buffed to with experience. Default is 200% of starting according to the wiki.
EDIT2:
http://df.magmawiki.com/index.php/DF2010:Creature_token has a list of some of the tokens you can add or remove from creatures.