for general information about cooperative education (Duales Studium) see Wefugee information here: https://www.wefugees.de/k/questions/1612
Basically there is no limitation of age if you want to study
If you finished a professional education in Syria you have to pass a formal procedure to consider whether training was equivalent to comparable training in Germany and whether your qualifications can be recognised. See more here http://bit.ly/2c7ORfP
Your local job center offers career counselings, ask for an appointment. I can provide you with a concrete adress if needed, if you tell us where you live In Germany right now.
If you are interested to improve your education as a dental laboratory technician via a cooperative education this information may be interesting for you: http://bit.ly/2c7Qnig
(German text, many links to further information, I did test only some of them to see if they work. See especially links of section "Studium im Bereich Zahntechnik").
Kind regards, Jan