Mortgage insurers and thus lenders are tightening their lending criteria for older borrowers, fanning talk that anybody over 35 may have fewer credit sourcing options in the future.Responsible lending guidelines in the new National Consumer Credit laws are themselves to blame for what may prove a new feature of the mortgage market.Lisa Montgomery, the chief executive of Resi Home Loans, said the new laws are doing their job and protecting people from being left with big mortgages and no income except a Centrelink pension in their old age."Last week our mortgage insurer rejected an application we took for an 80 per cent LVR loan from a 59-year-old woman with $20,000 in super."In that situation the borrower just couldn't demonstrate an exit strategy from the loan via investments, super, continued income or the sale of other assets."The 59-year-old mortgage applicant would "definitely" have been approved for a loan, Montgomery said, if the application was received prior to the new responsible lending guidelines.Mortgage insurers are telling lenders that the key to lending to over 45-year-olds is that the exit strategy at retirement from debt should now not include the sale of the primary place of residence, even if that is the source of the debt in question.Previously the application of the 59-year-old woman for an 80 per cent mortgage would have been a assessed on her income until retirement and, if required, sale of the house for, presumably, a capital gain.Montgomery said the new guidelines are a big step forward."I think, under responsible lending, the advice we have from funders and our insurers is that over about the age of 45 applicants need to be able show an exit strategy from a super balance or other family investments."Nobody wants to see stories of people being left with huge debts and just a government pension for their income."Having said that, thanks to compulsory superannuation, the average person will be able to demonstrate an exit strategy from their debt at retirement," said Montgomery.Families selling one house and moving to another could potentially be left without a home or the ability to get a new mortgage unless they organise their new loan and all their financial plans, up to and including their retirement, before selling their existing home.However, the average Australian superannuation balance for Australian men is less than $90,000, and just $53,000 for women.The average Australian aged between 55 and 64 has about $142,000 in super, according to Australian Bureau of Statistics' data compiled by the Australian Super Funds Association.But any mortgage applicant over 35 with little superannuation and no other investments must be rejected by banks, brokers and all other lenders for a 30-year residential mortgage, said Geoff Baldwin, CEO of WA-based real estate group ReMAX."The NCCP is effectively discriminating against some borrowers on the basis of age," said Baldwin."Lenders are running scared about this."