So where is the throttle butterfly when you crank any mower engine with a single control wire made in the last 30 years ?
WIDE OPEN
And on all of them the throttle has to go to WFO then on a bit further to engage the choke if it has a manual choke.
And that is from every factory, Honda, Briggs ,Kohler, Kawasaki,Suzuki, Loncin, Ducar.
All of them start with the throttle WFO
And this is for ride ons and walk behinds
As for thinking the engine will wear out prematurely because it starts up at full speed, you have been watching way to much TV.
Engine wear per minute can be highest during the 5 minutes of start up but it is the wear that happens in the 20 minutes of mowing running way too lean that does the damage.
In fact I doubt that many people would actually run the mower for more than 1 minute before actually mowing.
The next thing to consider is HOW THE OIL IS CIRCULATED.
If the mower has both an oil pump and a hollow crank shaft with oil outlets for the top, bottom & conrod bush then running the engine at a lower speed may reduce wear.
However wear is also SPEED related and an engine running slowly on a dry bore will wear more than an engine running quickly on a dry bore . it is all about load.
However most push mower engines have splash lubrication so if the engine is warmed up slowly then you will be starving the the top end and in particular the little end bearing for oil.
For oil to get to the little end it has to be picked up by the dipper then flung right up into the underside of the piston, fill the lubrication well then drip down into the little end.
The faster the engine is reving the more oil will be splashed around inside and the more oil will get to the underside of the piston.
Run your engine, just off stoping speed for a tank full of fuel and there is a very good chance you will sieze the engine.