"Lent began as a way for Catholics to remind themselves of the value of repentance," GotQuestions explains. "The austerity of the Lenten season was seen as similar to how people in the Old Testament fasted and repented in sackcloth and ashes (Esther 4:1-3; Jeremiah 6:26; Daniel 9:3)."
However, as time went on after the establishment of Lent, its observance became more sacramental, particularly within Roman Catholocism. "Many Catholics believe that giving something up for Lent is a way to attain God’s blessing," GotQuestions continues. "But the Bible teaches that grace cannot be earned; grace is 'the gift of righteousness' (Romans 5:17)."
"Also," the article adds, "Jesus taught that fasting should be done discreetly: 'When you fast, do not look somber as the hypocrites do, for they disfigure their faces to show men they are fasting. I tell you the truth, they have received their reward in full. But when you fast, put oil on your head and wash your face, so that it will not be obvious to men that you are fasting, but only to your Father, who is unseen' (Matthew 6:16-18). Jesus’ command to 'wash your face' seems to conflict with the practice of rubbing ashes on one’s face on Ash Wednesday."
This certainly isn't to say that fasting in itself is wrong—in fact, the Bible frequently speaks of all manner of fasting and prayer. As well, God is surely pleased when we repent of sinful habits or dependencies that draw us away from Him. And, of course, taking time to focus, meditate, and thank the Lord for his sacrificial death and glorious resurrection is a wonderful thing. However, there is no legitimate reason why each of these aspects of Lent should be restricted to a six-week period.
If we fast and pray, we should do so according to the leading of God and the conviction He gives us, not tradition alone. If we die to ourselves and root out sinful habits in our lives, it must be a continual, lifelong, sanctifying process, not a 40-day break. If we remember Jesus' death, descent, and resurrection, we must remember it every day of our lives, not just when it's "in season", for it is the reason we are able to have peace with God and life everlasting.
If you wish to learn more about the biblical approach to fasting and prayer, John Piper has written an incredible book on the subject, A Hunger for God: Desiring God Through Fasting and Prayer, in which he "invites you to turn from materialism and sharpen your appetite for God through prayer and fasting. [Piper's] exploration of fasting will help you understand how this ancient biblical practice can nourish your spiritual life and satisfy your longings."
As with many holidays in the liturgical calendar of Christian orthodoxy, a Christian is certainly free to observe Lent if he or she chooses to do so. "The key is to focus on repenting of sin and consecrating oneself to God," Got Questions concludes:
"Lent should not be a time of boasting of one’s sacrifice or trying to earn God's favor or increasing His love. God’s love for us could not be any greater than it already is."