Ah too many responses for a simple thing. To summarize:
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LD (Ladies Quota) Age does not matter and any number upto 6 per PNR can be booked. Upto 12 kids allowed to travel in LD quota.
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LB...
more... (Lower Berth) Quota can be applied if Lady above 45 is travelling alone (one person in one PNR). For that matter it is applicable to 60+ male travelling alone too.
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Ladies quota in generally in SL. I checked couple of samples and LD was only in SL.
May be for Full AC trains it exists in 3A and other AC classes. Not sure what exactly is the rule.