Few pointers for this strategy (i use it too)
1. Take maximum advantage of players not prolonging contracts to high profile players.
Got Tevez on free (end of contract), sold on half season to Barca for 23.5M pounds.
Got Asmir Begovic , sold on half season for 10.5M
Got Alex Song, sold on half season for 15M etc. etc.
2. Sell players min. 1.5 year before end of contract if you dont want to prolong it ( higher wages issue)
Max wage in my club ( Borussia Dortmund) is Goetze's..... 80k. Second best is Lars bender at 70k. NO ONE is worth 100k+ wages.
3. BUY high, sell higher.
Some players get ****** off on club league rating, their managers and get transfer requests. If player is well known. buy him, he'll be great asset for half season then resold.
Bought Hulk for 21M , sold 1 year later for 40.5M to Chelsea.
I'm at half season at my 5th season and this are my stats.
4. ALWAYS sell players on 48 months, preferably buy the for cash. Maximises your expences, lowers profit so you have less of that to tax, not sure too but i think that also means less money to pay for dividends. And your money is still coming in in small increments every month
Bought : 94 players for 190M
Sold : 56 players for 518M
Yearly spent for wages : 45.44M
P.S.
You have to consider 28 years barrier as optional thing because :
Different player positions on pitch degrade faster then others ( GK's dont lose points even in 33)
Tevez was 29 when he came to my club, 30 when he was sold for 23.5M so you have to take player reputation in respect too.
Age barrier is as good as you make it, my current inflow of regens and buying of them makes it available i rotate on age mark 26 or less.
Finally, make your game interesting and sell your good regens to your own league clubs