Nerve agents and substances causing injury to the skin and tissue are easily soluble in, and penetrate many different types of material, which renders decontamination more difficult. If chemical warfare (CW) agents have penetrated sufficiently deep, then toxic gases can be released from the material for long periods.
To be a jockey, there are no height limits, only weight limits. A rider can be of any height if they can still make weight, but it is still generally limited to fairly short individuals because of the limits on a person's body. Jockeys typically range from 5' to 5'7 in height. No need to lose any weight.
Learn how to ride a horse. Most trainers and racehorse farms don't have the time to teach basic riding; you'll need to learn that before engaging with them. Learn how to center, trot and walk before you set out to become a jockey. Learn to ride English. Most racehorses are ridden in English-style saddles.