Skimag.com has a list of discounts for seniors

Ski Area 60+ 65+ 70+ 75+ 80+ 90+
Cannon Mountain (NH) Free (must be NH resident)
Monarch (CO) $69/day (62+) $25 season pass (69+)
Gunstock (NH) $49 season pass
Shawnee (PA) Free
Mountain High (CA) $10 season pass
Pajarito (NM) Free
Sipapu (NM) Free
Spider Mountain (NM) Free
Swain Resort (NY) Free
Mt. Hood (OR Discount Discount Free
Taos (NM) Discount Discount Discount Free
Alta (UT) $50 season pass
Mammoth (CA) Free
Sugarbush (VT) Discount Midweek Pass Discount Midweek Pass Discount Midweek Pass Discount Free