Never had a speed gun to tell me how fast I could sling the ball down, (my prime years were 1976-86) but I reckon that my bowling lifespan mirrors many who end up turning their arm over for the love of the game.
So then, started as a young speed merchant. Moved on to that pace where it isn't as fast as you were but still nippy (fast medium or medium fast, dunno the technicalities of what should be first). Then medium pace (you tell everyone that medium pace bowling isn't becoming an average bowler as you need to find more guile to your deliveries. And the batsmen claim a moral victory when you are brought on cos they think they have seen off the attack bowlers). Then the knees and back start getting tweeky...you have to decide to finish there...but a life without turning your arm over once a week would be unbearable...and start bowling spinners BUT, at that faster speed like Derek Underwood. Then you turn 50 and just hoy down whatever your tired body can in senior/over 40 (age) matches.
The captain usually asks me to come on so as to bowl a few quick overs at the end of the oppositions innings so that everyone can get to the bar earlier!!