Government of India, Ministry of Railways, Railway Recruitment Board (RRB) conduct Junior Engineer recruitment exam time to time , as you want here I am telling its eligibility criteria and age limit :

Eligiblity
Three years Diploma in Civil Engineering/
Mechanical/ Electrical/ Electronics/ Manufacturing/
Mechatronics/ Industrial/ Machining/
Instrumentation & Control/ Tools & Machining/
Tools & Die Making/ Automobile/
Production Engineering or
B.Sc in Civil Engineering of three years duration
OR
(b) a combination of any sub stream of basic streams of
Civil Engineering from a Recognized University/ Institute.

Age Limit:
Applicants age should be between 18-32 years for Junior Engineer,

Relaxation of Upper age limit:
Sl No Category Age
relaxation
1 Scheduled Caste/ Scheduled Tribe 5 years
2 Other Backward Classes 3 years
3 Persons With Disabilities 10 years
4 Persons With Disabilities (OBC) 13 years
5 Persons With Disabilities (SC/ ST) 15 years
6 Widows, Divorced Women and Women Judicially separated
from Husband but not remarried 35 years (UR)
38 years (OBC)
40 years (SC/ ST)
7 Ex-Servicemen upto the extent of service rendered in Defence, plus 3 years, provided they have put in more than 6 months service after attestation
8 Serving Group “C” and erstwhile Group ‘D’ Railway Staff, Casual Labour and Substitutes 40 years (UR)
43 years (OBC)
45 years (SC/ ST)