What do you mean?
If you mean can you change his height from say, 5' 6" to 6' 1", then the answer is no.
If you mean you want him to start up in the air somewhere, then, yes.
Taking the player as an example:
player setpos [getpos player select 0, getpos player select 1, +100]
This will place the player in the same location as he is at present, but 100 metres up in the air.
Of course the fall would kill him.
Just change the +100 to whatever height you want.
Get the Official Command Reference from the Editors Depot.
It is a handy reference for the commands that are available.
Planck