When dealing with a headache, try boiling one cup of apple cider vinegar and one cup of water in a pot. Pour into a heat proof bowl and put on the table or other safe place that you can lean over the bowl and cover your head with a towel. Inhale the steam for a few minutes to bring some relief.
The warning on mine says not to use prior to 4 months of age. My son was in his Jolly Jumper from 3 months. The directions of use are that if they can confidently hold up their head then they are fine.
All children younger than 12 years and smaller than 150 cm (4 ft 11 in) must use a booster seat or child-safety seat appropriate to their weight. The Department of Transport advises that children continue to use a seat when they are 12 years or older but smaller than 150 cm (4 ft 11 in).