Hello

You don't need any age limit to become an interior designer. You can become an interior designer once you have set your goal to become one. All you need is your heart into it when your learning the course and little bit of training under someone who is expertise in this field. Once you grab both theorical and practical knowledge your set to start your own.

Some good colleges for interior designing:

CEPT Ahmedabad

APIED Vallbhvidyanagar Anand,

These can be followed by a course of construction management at NICMAR, Pune.

The following-

NID Ahmedabad,

Raffles Mumbai,

MIT Pune and

ISDI Mumbai (girls only)
I hope it will help you
Good luck.....