Size wasn't actually that important. It's not like 5 cms more will get you automatically far more likely to get killed then the other person also wearing bright uniforms and a big black hat. Research in the French Registers clearly show men of 'wrong' heights in various units, just like it clearly shows men without the necessary experience being recruited into the Guard.
Indeed, some people were sent in the Garde because their officer wanted to get rid of them ! (memories of Coignet)
About the experience, for example the Vélites de la Garde Impériale were specifically unexperimented men, but educated. This education was supposed to led them to an officer charge but first they had to learn to be a ranker in the Garde Impériale. Most of them (as Bourgogne wrote it) were very young men, teamed up with an old grenadier. Most of them saw their first battle at Eylau !
I like to think that, as in reenactement today, I would have been a light infantryman. I like the scouting duty, the "freedom" of not being oppressed in a big line, the pleasure of a good shot. Technically, i'm too tall to be a light infantry man and would probably end up as a dragoon. Considering I have an education, if I did survived the revolutionary wars, I can imagine I would have been Aide de Camp to a Colonel in 1796-1798. Probably followed by a post in the diplomacy as Caulaincourt. "Only if"