30 is fine, mid 30's okay (I was). Any older and you need to think a bit harder about what your getting yourself into.
Firstly, many airlines have a seniority list. Time to command could be 10-15 years or worse in the more established ones. Some of these airlines may never promote those that have joined in the last few years to the LHS given that the ICAO retirement age keeps on ebbing up and their skippers could only be in their 30's at present so have a long long time to go. Consideration may have to be given to being a professional co-pilot. It may not be everyones cup of tea. If you leave to join another airline then you start at the bottom of the rung and the process starts over.
Secondly, this really is a young persons game. Young and fancy free I would dare say. Having the ability to up sticks and move around the world would stand you in good stead. The following thread has some really useful insights into the sacrifices involved, particularly for those of us with a family and kiddies.
http://www.pprune.org/interviews-job...y-story-5.html