how old before a child can travel in front seat?

[Bronte]

I see lots of parents ferrying their children in front seats with child sat in booster seat.
Is this legal? I thought a child had to reach a certain height before they could sit in the front seat ...not be boosted to an artificial height. someone in the know please clarify.

height or age - though can't remember what age it is or which height. Differs between EU countries and not sure worldwide..?

No age limit in UK - babies can go in the front from birth if you are able to turn the airbags off (or if the car doesn't have them) - once a child is in a forward facing seat (which legally can be as soon as they reach 9kg - for babies on the highest percentile, this is around 4 or 5 months! Though hopefully nobody would actually recommend this) they can go in the front seat even if there is an active airbag.

Or height limit. Other countries do have restrictions though.

I had an idea its around 12 but not sure where i remember this from.