These ECB Directives apply as of 2016

Age                              Max. overs         Max. overs per spell per day
Up to 13                              5                                   10
U14, U15                             6                                   12
U16, U17, U18, U19        7                                   18

For the purpose of these Directives a fast bowler is defined as a bowler to whom a wicket keeper in the same age group would in normal circumstances stand back to take the ball.

Having completed a spell the bowler cannot bowl again, from either end, until the equivalent number of overs to the length of his* spell have been bowled from the same end. A bowler can change ends without ending his current spell provided that he bowls the next over that he legally can from the other end. If this does not happen his spell is deemed to be concluded. If play is
interrupted, for any reason, for less than 40 minutes any spell in progress at the time of the interruption can be continued after the interruption up to the maximum number of overs per spell for the appropriate age group.
If the spell is not continued after the interruption the bowler cannot bowl again, from either end, until the equivalent number of overs to the length of his spell before the interruption have been bowled from the same end. If the interruption is of 40 minutes or more, whether scheduled or not, the bowler can commence a new spell immediately.

In matches of 20 overs or less per team where the competition regulations only allow bowlers to bowl less than or equal to the number of overs specified as the maximum in a spell in the Directives the provisions requiring an equivalent number of overs from the same end to have elapsed before a subsequent spell can commence shall not apply (e.g. in any age group
competition where a maximum of 4 overs per bowler is allowed these may be bowled at any time in the innings irrespective of the number of spells bowled).

Once a bowler covered by these Directives has bowled in a match he cannot exceed the maximum number overs per day for his age group even if he subsequently bowls spin. He can exceed the maximum overs per spell
if bowling spin, but cannot then revert to bowling fast until an equivalent number of overs to the length of his spell have been bowled from the same end.

If he bowls spin without exceeding the maximum number of overs in a spell the maximum will apply as soon as he reverts to bowling fast. Captains, Team Managers and Umpires are asked to ensure that these Directives are
followed at all times.

For guidance it is recommended that in any 7 day period a fast bowler should not bowl more than 4 days in that period and for a maximum of 2 days in a row. Age groups are based on the age of the player at midnight on 31st August in the year preceding the current season.

*Any reference to he/his should be interpreted to include