It is completely up to the country doing the drafting.  According to international law, one must be at least 18 to fight, so, that would probably be the bottom age.  But, the top age is only limited by the country setting the rules - it might be 26, but, could just as easily be 46, or even 56.

Past experience has shown that draftees are not nearly as good soldiers as volunteers, so, few countries even have a draft these days.

Without an Act of Congress re-instating a Draft, nobody can be Drafted, regardless of age.

- and IF they ever do re-instate it, things are going to be interesting since (at their own insistence) Women can now serve in Combat Units...Equal = Equal, Not Special

Asthma is PDQ for military service. If you have it you will fail the physical.

They set up a lottery for the order.

First, there is no draft at this time in the US.  Secondly, in the event of a national emergency, the draft can return and the guidelines at that time will be defined based on need.  Third, recall that during WWII, when manpower was badly needed, the age for drafting was raised to 35 years of age and once in, you were in for the duration + 6 months with a minimum tour of 24 months.  Fourth, should this be returned due to a substantial national emergency, the rules at that time will be defined to reflect the need and each local board will have some flexibility in the guidelines to permit them to deliver their quota of manpower.  Fifth, the military is a lot more technical and sophisticated now and the old model of someone with less than a high school education is no longer the case.  While lightly educated are needed for non-technical needs like food service, laundry, janitorial, and similar tasks, these needs might equally be filled by other means.  I see someone like you more of a nuisance and problem than an asset so you will probably, if drafted, end up in the brig or given a dishonorable discharge. 

What draft????????

The draft was dissolved over 30 years ago