Is this age the only opportunity for salvation? The majority of mainstream Protestant churches in the U.S. proclaim this age is the only opportunity for salvation.  There's a prominent minority, mostly non-denominational, that claim the period after the second resurrection is another opportunity for salvation.

The implications today concern evangelism efforts.  My experience with Baptist churches are they need to reach people before they die in THIS age, otherwise they are lost forever.  My experience with the non-denominational churches (who believe otherwise) are many simply are not called in this age (e.g. John 6:44), they will be given a chance for salvation in the second resurrection (e.g. Rev 20:5, barring the obvious that those who've received, then rejected Christ, are impossible to redeem thereafter, e.g. Heb 6:6).

Although I was reared around the Baptist and Methodist churches, I don't know their scriptural basis for their belief if you die in the life never knowing Christ you are lost forever.  The churches proclaiming that is not the case point out a lot of scriptural support.  

Some examples: 


the Lev 23 Holy Days, an annual reminder of the milestones in God's annual plan of salvation for mankind.  For example, TO THE DAY Christ was crucified on Passover, TO THE DAY the Holy Spirit was made widely available to mankind on Pentecost.  To come: Trumpets (Christ's return), Atonement (Satan's binding), the Feast of Tabernacles (1,000 year of Christ on earth), and the Last Great Day (8th day of Tabernacles, is the Great White Throne Judgement).
birthright and firstfruits theme throughout scripture.  This is way too long to post here.  But, I'll reply if requested.  But, it is throughout scripture from Genesis to Revelations.
lots of scripture showing God is not calling everyone in this age, even causing them to be spiritually blind and deaf so that they cannot respond to the gospel.
and various other scriptures supporting this, e.g. Isaiah 49:8's proper translation is "a" day of salvation, not "the" day.


and more.  

My question: what is the Baptist/Methodist/same Protestant scriptural basis the age we are currently living in is the only age for salvation?
What is the Biblical basis for the Baptist belief in a singular day of salvation

Here is a description of one Baptist view.


Those who were saved before the cross are saved by faith, but receive their eternal life at the first resurrection.



  Hebrews 11:39-40  And these all, having obtained a good report through
  faith, received not the promise:  God having provided some better
  thing for us, that they without us should not be made perfect.
  
  Revelation 20:6  Blessed and holy is he that hath part in the first
  resurrection: on such the second death hath no power, but they shall
  be priests of God and of Christ, and shall reign with him a thousand
  years.



Those who trust in Jesus since the cross have immediate eternal life.



  John 5:24  Verily, verily, I say unto you, He that heareth my word,
  and believeth on him that sent me, hath everlasting life, and shall
  not come into condemnation; but is passed from death unto life.


Those who died in faith before the cross will have a single day of salvation (when they receive eternal life). Those who die after the cross each have a particular day when they are saved. 


The second death is reserved for those of the second resurrection. This is a resurrection for the judgment of works.