I am 58 years old. Bald in the front n nedd hair transplant. I habe checked and advised that i may need about 40,000 gratfs. I need to know if i can the procedure in Chennai n how long it will take n the estimated costs

Yes your procedure can be done . You need to share scalp pics to hair transplant surgeon to get idea about your donor area and graft requirement.
Cost of hair transplant will be 20-25 Rs per graft so for 4000 grafts it will be 80000 to 1 lac Rs

40000 graft is a myth or may be wrongly heard. At max around 2500-3500 grafts can be implanted in one session and maximum 4000-4500 grafts may be implanted in two sessions. I have no idea about Chennai but surgery might take upto 6-8 hrs. and this varies from clinic to clinic.