It is common knowledge that soccer players possess differents skills and capabilities as they develop.
Very young players have minimal fine motor skills, very little understanding of team play or spacial awareness and a very low concentration span.  As players mature,  all of these attributes improve, and by the time the players reach 14 or 15, they are nearly fully developed, and so more sophisticated training sessions can be conducted. 

There is absolutely no point trying to get players of 5 years of age to play like a team of 15 year olds, and so the training and nature of the sessions must be age appropriate.

It is fair to say that in all age groups, training sessions must be
  1. Engage players, and make players want to come to training
  2. Have some competetive nature
  3. Encourage team spirit
  4. Be appropriate for the age group in terms of skills/drills and session time

Recommended number of sessions and session times

Age Pre Season
Sessions
per week
During season
Sessions
per week
Session Time
Under 9 2 1 60 minutes
9-12 2 1- 2 75 minutes
12+ 3 2 90 minutes

Recommended 15 week program

The following table shows the types of sessions that should be conducted for various age groups covering a 15 week period.
Note for the older players 2 sessions a week is recommended.  If you have a different number training weeks , then modify the table to suit, trying to ensure the same ratios of Dribbling, Passing, Shooting, Headcing etc

Week Ages 4-9 Ages 9-12 Age12+
1 Dribbling Dribbling
i) Passing
ii) Possession and Defending
2 Dribbling Dribbling i) Passing
ii) Possession and Defending
3 Dribbling Dribbling i) Passing
ii) Possession and Defending
4 Dribbling Kicking - push pass
i) Passing
ii) Fitness Assessment
5 Kicking - push pass
Kicking - instep
i) Passing
ii) Receiving the ball
6 Kicking - instep
Passing  i) Passing
ii) Receiving the ball
7 Passing Passing  i) Passing
ii) Receiving the ball
8 Passing Passing i) Passing
ii)Fitness Assessment
9 Passing
Shooting  i) Ball Control
ii) Dribbling
10 Passing
Shooting i) Ball Control
ii) Dribbling
11 Shooting
Heading
i) Ball Control
ii) Dribbling
12 Shooting
Ball Control  i) Mobility and Agility
ii) Heading
13 Ball Control Ball Control i) Mobility and Agility
ii) Shooting
14 Ball Control Ball Control  i) Mobility and Agility
ii) Shooting
15 Ball Control Ball Control  i) Mobility and Agility
ii) Shooting