Hello welcome to careers360.

If you are 12th class the .Join engineering and simultaneously you can learn application development  if you are interested in.

Rather than Mobile development there are lot of courses like web development, artificial intelligence, machine learning..

So after 5yrs we can not expect how the technology will be even android may wanish is not my assumption there is talk regarding that.

So the conclusion is don't get stick to Mobile development. Learning Mobile development is fine but don't stick to that also learn artificial intelligence and machine learning it is the future is.

Hope this is helpful.

Good luck!