Colleges in Bihar

No, as a matter of fact find ways to use your background. Being a science student will help with entrance exams. Try to keep up with the latest news and find ways to work on your design/sketching skills. Make a list of all the deadlines for the college's you want to apply to make sure you don't miss them.

Yes, you can either do a fashion designing Diploma or a certificate course. If you have or when you get enough technical experience you can start doing Internships to get experience/make contacts. Find local colleges around you so you can hit the ground running.

Cabin Crew Training Course allows you to get groomed and ready for the interviews which various hiring airlines conduct from time to time. Usually all such Academies groom candidates in order to become presentable in the interview. Both Avalon and PTC are comparable academies, because None provides placements. No such academy provides placements for that matter. They only groom you and help you in getting notified about vacancy announcements.

You can email the university asking them about this because the age limit criteria is over and I think they should also get over with the limit criteria.
Good luck.

Please contact the college officials to know about the fees: http://www.avalonacademy.in.